tag:blogger.com,1999:blog-45412715522029316742024-03-10T19:50:33.854+00:00Blackwater SkiesAstronomy & Astro-imaging from East of the MeridianUnknownnoreply@blogger.comBlogger38125tag:blogger.com,1999:blog-4541271552202931674.post-76977803213432089722016-09-14T22:38:00.001+01:002016-09-29T11:09:30.722+01:00Monster Prominence 3.5 Hour Animation (Ha)<span style="font-family: "arial" , "helvetica" , sans-serif;">My biggest animation yet, with a 100,000km prominence:</span><br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjyqiKcv9L7jsb85aecNzgyVoZIS0ai8b9k4zZf5jzz20Zy-90EGJiLO1ERfjA6F70AW4H020o1rfL7Uh0iTVhjhQmTcLBd53bEl00yLSFXLNjZe2RcLT_n-kkK_lIujHKQUB34TXh_z_w/s1600/Final.gif" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjyqiKcv9L7jsb85aecNzgyVoZIS0ai8b9k4zZf5jzz20Zy-90EGJiLO1ERfjA6F70AW4H020o1rfL7Uh0iTVhjhQmTcLBd53bEl00yLSFXLNjZe2RcLT_n-kkK_lIujHKQUB34TXh_z_w/s1600/Final.gif" /></a></div>
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<b style="font-family: arial, helvetica, sans-serif;"><span style="color: orange;">Scope:</span></b><span style="font-family: "arial" , "helvetica" , sans-serif;"> Lunt LS60THa/B1200CPT, 2x Barlow</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Camera:</span></b> ZWO ASI174MM, FireCapture</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Mount:</span></b> Sky-Watcher NEQ6, EQMod</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Processing:</span></b> AutoStakkert! 2, PixInsight 1.8, best 25% of 500 frames, 174 frames, 30s intervals.</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Date: </span></b>11th September 2016, 09:52 - 13:17</span><span style="font-family: "arial" , "helvetica" , sans-serif;">BST (08:52 - 12:17UT)</span>Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4541271552202931674.post-89386430021298978342016-09-10T18:08:00.002+01:002016-09-29T11:09:15.931+01:00Prominence Animation Ha 3rd September 2016<span style="font-family: "arial" , "helvetica" , sans-serif;">Animation of prominences with solar disk masked:</span><br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiNEd9qUKwzlHFP5WOgtA5RJfqQxJrf14trgGGPXOr19XQZkoSXT5Ts4virHNFbxKEhxP5llPJyxkr7sy4LfeYmTfEuUfT8X5tCVheGArOv-RoqUs1cED85xWq5qqhqzsyEKJBtvMQYo1I/s1600/Final.gif" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="128" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiNEd9qUKwzlHFP5WOgtA5RJfqQxJrf14trgGGPXOr19XQZkoSXT5Ts4virHNFbxKEhxP5llPJyxkr7sy4LfeYmTfEuUfT8X5tCVheGArOv-RoqUs1cED85xWq5qqhqzsyEKJBtvMQYo1I/s640/Final.gif" width="640" /></a></div>
<b style="font-family: arial, helvetica, sans-serif;"><span style="color: orange;">Scope:</span></b><span style="font-family: "arial" , "helvetica" , sans-serif;"> Lunt LS60THa/B1200CPT, 2x Barlow</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Camera:</span></b> ZWO ASI174MM, FireCapture</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Mount:</span></b> Sky-Watcher NEQ6, EQMod</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Processing:</span></b> AutoStakkert! 2, PixInsight 1.8, best 25% of 500 frames, 41 frames, 30s intervals.</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Date: </span></b>3rd September 2016, 09:52 - 10:45</span><span style="font-family: "arial" , "helvetica" , sans-serif;">BST (08:52 - 09:45UT)</span>Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4541271552202931674.post-86557890726471554732016-09-06T18:12:00.002+01:002016-09-29T11:09:00.435+01:00Animation of AR12585 Ha 3rd September 2016<span style="font-family: "arial" , "helvetica" , sans-serif;">Animation of AR2585, plus filament and prominences.</span><br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjHsjA0Lt9bvjqE2nCWdLDhAkrdCNJZOQUnI94O86lh0j0wnaaqCZzxGTcTIwDsKwobZsXijzWTvYizfm1KgfgKda55jam-CoxC2YFueSsVhk1oqIzkDk_Eoe-7oBNrIpMfWilSXoi8oSQ/s1600/Animation.gif" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjHsjA0Lt9bvjqE2nCWdLDhAkrdCNJZOQUnI94O86lh0j0wnaaqCZzxGTcTIwDsKwobZsXijzWTvYizfm1KgfgKda55jam-CoxC2YFueSsVhk1oqIzkDk_Eoe-7oBNrIpMfWilSXoi8oSQ/s640/Animation.gif" width="586" /></a></div>
<span style="font-family: "arial" , "helvetica" , sans-serif;"><br /></span><b style="font-family: arial, helvetica, sans-serif;"><span style="color: orange;">Scope:</span></b><span style="font-family: "arial" , "helvetica" , sans-serif;"> Lunt LS60THa/B1200CPT, 2x Barlow</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Camera:</span></b> ZWO ASI174MM, FireCapture</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Mount:</span></b> Sky-Watcher NEQ6, EQMod</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Processing:</span></b> AutoStakkert! 2, PixInsight 1.8, best 25% of 500 frames, 31 frames, 30s intervals.</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Date: </span></b>3rd September 2016, 08:34 - 09:19</span><span style="font-family: "arial" , "helvetica" , sans-serif;">BST (07:34 - 08:19UT)</span>Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4541271552202931674.post-34399969250685257952016-09-03T17:10:00.001+01:002016-09-29T11:04:25.981+01:00AR12585 Ha 3rd September 2016<span style="font-family: Arial, Helvetica, sans-serif;">Great view this morning with prominences, filaments, sunspots and plages.</span><br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhXCDR8nageEE-HUTIrEbqPWUAtjYF3ZPIF9oZfBjxdD5XV-nsRzfq0Jktv7FH8C22xhKdgzmvLZv_WRenT5BIjU2zKrLaNbWhJTE9m38WNKNUuTU0kw3Mhnj7Wrc9-0VHg0M35mazG8ek/s1600/Sun_Full_16_09_03_08_21_07_g4_ap4200_Drizzle15_Invert_Labelled.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhXCDR8nageEE-HUTIrEbqPWUAtjYF3ZPIF9oZfBjxdD5XV-nsRzfq0Jktv7FH8C22xhKdgzmvLZv_WRenT5BIjU2zKrLaNbWhJTE9m38WNKNUuTU0kw3Mhnj7Wrc9-0VHg0M35mazG8ek/s640/Sun_Full_16_09_03_08_21_07_g4_ap4200_Drizzle15_Invert_Labelled.png" width="635" /></a></div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEggTM9SDyNFrrqzyLKeDpK0Pp2EDq_y39aFKzbXDYLkNXKYhf5MwjK-JOhb-CmYset4LnyHlhL5-9RwForBbYAoK_OEKt5gz7GCjxjLaUvr62AUl3KAWwzaf8JtLD0u2dlk02Qacfha2S4/s1600/Sun_Full_16_09_03_08_21_07_g4_ap4200_Drizzle15_Labelled.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEggTM9SDyNFrrqzyLKeDpK0Pp2EDq_y39aFKzbXDYLkNXKYhf5MwjK-JOhb-CmYset4LnyHlhL5-9RwForBbYAoK_OEKt5gz7GCjxjLaUvr62AUl3KAWwzaf8JtLD0u2dlk02Qacfha2S4/s640/Sun_Full_16_09_03_08_21_07_g4_ap4200_Drizzle15_Labelled.png" width="634" /></a></div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgPIDytiCJtOLxBsr1OnJwpnt8JQGdmgn1WlYpa8IDfv4OYMNmBOP6jB0TVeQo64oaTRo3YQM0zWvBfqQPPmO5BNHWVGbNchJtNv7m9Rwag4pcuN7VsIXBR8jUFdKbIT-LCz2lvRgsQdJ4/s1600/Sun_Full_16_09_03_08_04_37_g4_ap2509_Drizzle15_Invert_Labelled.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgPIDytiCJtOLxBsr1OnJwpnt8JQGdmgn1WlYpa8IDfv4OYMNmBOP6jB0TVeQo64oaTRo3YQM0zWvBfqQPPmO5BNHWVGbNchJtNv7m9Rwag4pcuN7VsIXBR8jUFdKbIT-LCz2lvRgsQdJ4/s640/Sun_Full_16_09_03_08_04_37_g4_ap2509_Drizzle15_Invert_Labelled.png" width="640" /></a></div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh3XJ3fDJ-SWxsIIe536x52_lJXQeoYXaYYSxVS9BfbXMcct4WiM2hRQ6HfF2tppWO45JhDnTiKLh89nYf04pcIDgkIg-uut19gnj_k_sGVvPUtLUqU2ayAybl3ofU0MoBq9lQoOP3ThWs/s1600/Sun_Full_16_09_03_08_04_37_g4_ap2509_Drizzle15_Labelled.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh3XJ3fDJ-SWxsIIe536x52_lJXQeoYXaYYSxVS9BfbXMcct4WiM2hRQ6HfF2tppWO45JhDnTiKLh89nYf04pcIDgkIg-uut19gnj_k_sGVvPUtLUqU2ayAybl3ofU0MoBq9lQoOP3ThWs/s640/Sun_Full_16_09_03_08_04_37_g4_ap2509_Drizzle15_Labelled.png" width="640" /></a></div>
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<b style="font-family: arial, helvetica, sans-serif;"><span style="color: orange;">Scope:</span></b><span style="font-family: "arial" , "helvetica" , sans-serif;"> Lunt LS60THa/B1200CPT, (2x Barlow for close-up images)</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Camera:</span></b> ZWO ASI174MM, FireCapture</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Mount:</span></b> Sky-Watcher NEQ6, EQMod</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Processing:</span></b> AutoStakkert! 2, PixInsight 1.8, best 75% of 500 frames</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Date: </span></b>3rd September 2016, 08:04 - 08:21</span><span style="font-family: arial, helvetica, sans-serif;">BST (07:04 - 07:21UT)</span>Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4541271552202931674.post-44684778646411257872016-07-17T16:59:00.002+01:002016-09-29T11:05:48.989+01:00AR12565/67 Ha 17th July 2016<span style="font-family: "arial" , "helvetica" , sans-serif;">Seeing was not so great this afternoon, but I took the first decent opportunity since May to grab these:</span><br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhuKlUFB4ste_CoFTh8W7mi-akG-YJbhDdNGLctHvBOxZOvcQstF6fR6ZKNSFv39T-rDp_XEeSkv17OSkB_S32MKInPCIxPgYVGOo-v00kpt2ltkNu0cy3c5f7-Z2E0Jh2V8lPkvZHJERs/s1600/Sun_Full_16_07_17_14_16_11_g4_ap3628_Drizzle15_final.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhuKlUFB4ste_CoFTh8W7mi-akG-YJbhDdNGLctHvBOxZOvcQstF6fR6ZKNSFv39T-rDp_XEeSkv17OSkB_S32MKInPCIxPgYVGOo-v00kpt2ltkNu0cy3c5f7-Z2E0Jh2V8lPkvZHJERs/s640/Sun_Full_16_07_17_14_16_11_g4_ap3628_Drizzle15_final.png" width="640" /></a></div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgurGZE1wmTjWAeun0kLf0MPUib0-HH-LFbinXzkwF57048EMY20pVUIrQkVpsRGxjNEw0iq8lMUt6knf2ee9otpkWmGFuSReeXsFYxitjVISLylJHenB8tpIJPT7KJfS5zhjKHG73_VRY/s1600/Sun_Full_16_07_17_14_16_11_g4_ap3628_Drizzle15_final_colour.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgurGZE1wmTjWAeun0kLf0MPUib0-HH-LFbinXzkwF57048EMY20pVUIrQkVpsRGxjNEw0iq8lMUt6knf2ee9otpkWmGFuSReeXsFYxitjVISLylJHenB8tpIJPT7KJfS5zhjKHG73_VRY/s640/Sun_Full_16_07_17_14_16_11_g4_ap3628_Drizzle15_final_colour.png" width="640" /></a></div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg9eYv5fLxZavMiWIfy4k-b1Ksf5LXzg9W20LOZa9hscTYX6ok_T6WktsY9Qp8Y8M627JXu53Esk3gTSwXw7SYSmOdAsO97EAIxEqdq1wDrAHJ3YG2H9qCff3Tke_5bh5OAwVm2Vr5pFWY/s1600/Sun_Full_16_07_17_14_16_11_g4_ap3628_Drizzle15_final_invert.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg9eYv5fLxZavMiWIfy4k-b1Ksf5LXzg9W20LOZa9hscTYX6ok_T6WktsY9Qp8Y8M627JXu53Esk3gTSwXw7SYSmOdAsO97EAIxEqdq1wDrAHJ3YG2H9qCff3Tke_5bh5OAwVm2Vr5pFWY/s640/Sun_Full_16_07_17_14_16_11_g4_ap3628_Drizzle15_final_invert.png" width="640" /></a></div>
<span style="font-family: "arial" , "helvetica" , sans-serif;"><br /></span>
<b style="font-family: arial, helvetica, sans-serif;"><span style="color: orange;">Scope:</span></b><span style="font-family: "arial" , "helvetica" , sans-serif;"> Lunt LS60THa/B1200CPT, 2x Barlow</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Camera:</span></b> ZWO ASI174MM, FireCapture</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Mount:</span></b> Sky-Watcher NEQ6, EQMod</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Processing:</span></b> AutoStakkert! 2, PixInsight 1.8, best 25% of 500 frames</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Date: </span></b>17th July 2016, 15:11BST (14:11UT)</span>Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4541271552202931674.post-38374008601413340002016-06-25T14:54:00.003+01:002016-09-29T11:06:10.067+01:00Another Mercury Transit Image<span style="font-family: "arial" , "helvetica" , sans-serif;">Another Mercury transit image. I've adjusted my processing routine to add MLT to the process, and trying out a different false colour scheme.</span><br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj5qTXutXEj6z-yeHNQlaxYoQRupfRIMBBfjpOKQUoObP28h0aPJBVDXuMJs7dxESm7eoouRTNGyrYCb7gNjZlrJC8pKfjdqRwSk3UJkGfdkGkT8-x7EEQ23Okv2fl5WsXqPFJKRzhp2e0/s1600/Sun_Full_16_05_09_13_48_40_g4_ap1599_Drizzle15_final_labelled.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="634" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj5qTXutXEj6z-yeHNQlaxYoQRupfRIMBBfjpOKQUoObP28h0aPJBVDXuMJs7dxESm7eoouRTNGyrYCb7gNjZlrJC8pKfjdqRwSk3UJkGfdkGkT8-x7EEQ23Okv2fl5WsXqPFJKRzhp2e0/s640/Sun_Full_16_05_09_13_48_40_g4_ap1599_Drizzle15_final_labelled.png" width="640" /></a></div>
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<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Scope:</span></b> Lunt LS60THa/B1200CPT</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Camera:</span></b> ZWO ASI174MM, FireCapture</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Mount:</span></b> Sky-Watcher NEQ6, EQMod</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Processing:</span></b> AutoStakkert! 2, PixInsight 1.8, best 75% of 500 frames</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Date: </span></b></span><span style="font-family: "arial" , "helvetica" , sans-serif;">9th May 2016, 13:48BST (13:48UT)</span>Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4541271552202931674.post-44570768079943569872016-05-09T14:38:00.001+01:002016-09-29T11:03:01.597+01:00Transit of Mercury, 9th May 2016<span style="font-family: Arial, Helvetica, sans-serif;">Mercury begins its transit across the face of the sun.</span><br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEja54pu3Iy1PIRir2C6OF2jlz_cfXFD2P3WVC_VfXmarrlnY_WwWdWeI0GNKGWSSPLaByehwMI7KRWcaB214rOgoMTP7F5DmwRuU0UzN1VYkC6aVWrTZyAbCnW1FNNBV3N0K2CW3Z-7APs/s1600/Sun_Full_16_05_09_11_14_38_g3_ap3531_Drizzle15_Invert_Final_Labelled.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEja54pu3Iy1PIRir2C6OF2jlz_cfXFD2P3WVC_VfXmarrlnY_WwWdWeI0GNKGWSSPLaByehwMI7KRWcaB214rOgoMTP7F5DmwRuU0UzN1VYkC6aVWrTZyAbCnW1FNNBV3N0K2CW3Z-7APs/s640/Sun_Full_16_05_09_11_14_38_g3_ap3531_Drizzle15_Invert_Final_Labelled.png" width="634" /></a></div>
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<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Scope:</span></b> Lunt LS60THa/B1200CPT</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Camera:</span></b> ZWO ASI174MM, FireCapture</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Mount:</span></b> Sky-Watcher NEQ6, EQMod</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Processing:</span></b> AutoStakkert! 2, PixInsight 1.8, best 25% of 500 frames</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Date: </span></b></span><span style="font-family: arial, helvetica, sans-serif;">9th May 2016, 12:14BST (11:14UT)</span>Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4541271552202931674.post-8401497172494968472016-05-09T11:02:00.000+01:002016-09-29T11:02:36.825+01:00AR12541/42/43 Ha 8th May 2016<span style="font-family: "arial" , "helvetica" , sans-serif;">Detail from yesterday.</span><br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjMlBdOthdUWgbtUIttGz2mj8fVfYsN24aTkojeAAa4sQRTH0ozUYognpPxoOYrtJ0ExQ6f6x2TzRWAgEdKeIZMbn5qpA-8BZRlk1LkAffKb8TQCeWpHlRRxIE6x2yK75mJJAVejdeEDck/s1600/Detail_09_31.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="624" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjMlBdOthdUWgbtUIttGz2mj8fVfYsN24aTkojeAAa4sQRTH0ozUYognpPxoOYrtJ0ExQ6f6x2TzRWAgEdKeIZMbn5qpA-8BZRlk1LkAffKb8TQCeWpHlRRxIE6x2yK75mJJAVejdeEDck/s640/Detail_09_31.png" width="640" /></a></div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiK6uUAE7wMHEHaqs8YMgkyhc70TjpNSoJPa_8vJfRfLK-jHIiy6cGO3SvRKMqCdNd4LzIVRI_Digsty0Hohu514aPHVcfgeW7PGtTUmodyCrUwqsT7Spo-MaHRaojGA7dnUplClZwrpZY/s1600/Detail_09_31_Invert.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="624" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiK6uUAE7wMHEHaqs8YMgkyhc70TjpNSoJPa_8vJfRfLK-jHIiy6cGO3SvRKMqCdNd4LzIVRI_Digsty0Hohu514aPHVcfgeW7PGtTUmodyCrUwqsT7Spo-MaHRaojGA7dnUplClZwrpZY/s640/Detail_09_31_Invert.png" width="640" /></a></div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiGlxWoSJDKBiq7I6S2P-PnBqioBV2rU2Zo3B4KO8qX4OTsI6B7UginiY0lOCLZRKosy_9zFPxANt8KLRo8MfnU3_ElZ-ZtcuGUqynLVMdFgXNTr3Y06n7TE2yiQLUwemi6qs5B6CP3CaA/s1600/Detail_09_31_Mono.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="624" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiGlxWoSJDKBiq7I6S2P-PnBqioBV2rU2Zo3B4KO8qX4OTsI6B7UginiY0lOCLZRKosy_9zFPxANt8KLRo8MfnU3_ElZ-ZtcuGUqynLVMdFgXNTr3Y06n7TE2yiQLUwemi6qs5B6CP3CaA/s640/Detail_09_31_Mono.png" width="640" /></a></div>
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<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Scope:</span></b> Lunt LS60THa/B1200CPT, 2x Barlow</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Camera:</span></b> ZWO ASI174MM, FireCapture</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Mount:</span></b> Sky-Watcher NEQ6, EQMod</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Processing:</span></b> AutoStakkert! 2, PixInsight 1.8, best 25% of 1,000 frames</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Date: </span></b>8th May 2016, 09:31BST (08:31UT)</span>Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4541271552202931674.post-22741172088300377862016-05-02T17:19:00.002+01:002016-05-02T17:32:50.343+01:00Solar UFO (Or maybe just a balloon!)<div class="separator" style="clear: both; text-align: left;">
<span style="font-family: "arial" , "helvetica" , sans-serif;">I caught a UFO crossing the sun on Saturday. Taken at 08:38BST, 30th April 2016. It was moving fairly fast so I had trouble tracking it as it took me by surprise.</span></div>
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<iframe allowfullscreen='allowfullscreen' webkitallowfullscreen='webkitallowfullscreen' mozallowfullscreen='mozallowfullscreen' width='320' height='266' src='https://www.blogger.com/video.g?token=AD6v5dyfb4aXPivDIPY4A2MEskJpd_bOVk7GhqiY7rv3JNCYx4C8xU1De1lWiB_8MQlE-MZlm9i7pcFBZ3iPeUaZaQ' class='b-hbp-video b-uploaded' frameborder='0'></iframe></div>
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<span style="font-family: "arial" , "helvetica" , sans-serif;">No satellites were predicted to transit the Sun from my location at that time. Sadly upon aligning, stacking and processing multiple frames from the video, it looks very much like a party balloon:</span></div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhwAC3LTtGCm8QOL2ASMifsUmXrr-eD1M84q7S98YtNAm_lz5zdDP-hYxvMWZrj-KMSxN12qVFF5FAYM5SzrgMMCiIcaUTOubXX_aNLZefUMWd2O_9Ca1WPVa1n_DKXmCJevy9bIFIRxCM/s1600/Alig_g3_ap5_Drizzle15_best.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhwAC3LTtGCm8QOL2ASMifsUmXrr-eD1M84q7S98YtNAm_lz5zdDP-hYxvMWZrj-KMSxN12qVFF5FAYM5SzrgMMCiIcaUTOubXX_aNLZefUMWd2O_9Ca1WPVa1n_DKXmCJevy9bIFIRxCM/s1600/Alig_g3_ap5_Drizzle15_best.png" /></a></div>
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<span style="font-family: "arial" , "helvetica" , sans-serif;"><b style="font-family: arial, helvetica, sans-serif;"><span style="color: orange;">Scope:</span></b><span style="font-family: "arial" , "helvetica" , sans-serif;"> </span><span style="font-family: "arial" , "helvetica" , sans-serif;">Lunt LS60THa/B1200CPT, 2x Barlow</span></span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><span style="color: orange;"><b>Camera:</b></span> ZWO ASI174MM, FireCapture</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Mount</span></b>: Sky-Watcher NEQ6, EQMod</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Processing:</span></b> AutoStakkert! 2, PixInsight 1.8</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Date:</span></b> 30th April 2016, 08:38BST (07:38UT)</span>Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4541271552202931674.post-12282238366155761012016-05-02T15:28:00.001+01:002016-05-02T17:19:54.505+01:00Sun - AR12535/36/38 Ha 30-05-2016<span style="font-family: "arial" , "helvetica" , sans-serif;">A close up from Saturday. Looks like I am getting some banding with the 2x Barlow so may need to start taking flats.</span><br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEixHyx_2z_JolSxwbvstbZQku1DF5sOLxLtKQ9advn6YkQ2mMM4NEv_pOJR55q6N_5KqUxhdAWt2DKydwIUGZBMveNKHaQL34WzRWcXrkUypFoDIka2AFwB8YrCUcFY43RVPj2UeCf4nfw/s1600/Sun_Full_16_04_30_08_41_36_g3_ap1306_Drizzle30.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEixHyx_2z_JolSxwbvstbZQku1DF5sOLxLtKQ9advn6YkQ2mMM4NEv_pOJR55q6N_5KqUxhdAWt2DKydwIUGZBMveNKHaQL34WzRWcXrkUypFoDIka2AFwB8YrCUcFY43RVPj2UeCf4nfw/s640/Sun_Full_16_04_30_08_41_36_g3_ap1306_Drizzle30.png" width="640" /></a></div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgO0hZHz1XhPs97Vu9o4Z9JCdK0QcFacVHrJYI3Qswdx85BxmOn4bemqgTy8qojGTZeYjThLHNisVVVzhHcNBsk0JU4zh2S5TqCaOcvgkxGTqDThXQjnntFoMGlrCkPgiIBHK5aoNkAKYE/s1600/Sun_Full_16_04_30_08_41_36_g3_ap1306_Drizzle30_Grey.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgO0hZHz1XhPs97Vu9o4Z9JCdK0QcFacVHrJYI3Qswdx85BxmOn4bemqgTy8qojGTZeYjThLHNisVVVzhHcNBsk0JU4zh2S5TqCaOcvgkxGTqDThXQjnntFoMGlrCkPgiIBHK5aoNkAKYE/s640/Sun_Full_16_04_30_08_41_36_g3_ap1306_Drizzle30_Grey.png" width="640" /></a></div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg8jkkgaxR4lGAcJQZ5If7zd6VI-m4Hwi3MOheYZAj_vNnHnF9O18CGdKDVXMflKo5WoxaFz6bwMp8lUJKKwHwFX5b1pW3TV2Q6X-jrrcVv-D24OXCNO8Olu-JYZj-Oon6Qklv83wcwiTA/s1600/Sun_Full_16_04_30_08_41_36_g3_ap1306_Drizzle30_Invert.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg8jkkgaxR4lGAcJQZ5If7zd6VI-m4Hwi3MOheYZAj_vNnHnF9O18CGdKDVXMflKo5WoxaFz6bwMp8lUJKKwHwFX5b1pW3TV2Q6X-jrrcVv-D24OXCNO8Olu-JYZj-Oon6Qklv83wcwiTA/s640/Sun_Full_16_04_30_08_41_36_g3_ap1306_Drizzle30_Invert.png" width="640" /></a></div>
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<span style="font-family: "arial" , "helvetica" , sans-serif;"><b style="font-family: arial, helvetica, sans-serif;"><span style="color: orange;">Scope:</span></b><span style="font-family: "arial" , "helvetica" , sans-serif;"> </span><span style="font-family: "arial" , "helvetica" , sans-serif;">Lunt LS60THa/B1200CPT, 2x Barlow</span></span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><span style="color: orange;"><b>Camera:</b></span> ZWO ASI174MM, FireCapture</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Mount</span></b>: Sky-Watcher NEQ6, EQMod</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Processing:</span></b> AutoStakkert! 2, PixInsight 1.8</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Date:</span></b> 30th April 2016, 08:41BST (07:41UT)</span><br />
<b style="font-family: arial, helvetica, sans-serif;"><span style="color: orange;">Frames:</span></b><span style="font-family: "arial" , "helvetica" , sans-serif;"> Best 15% of 1,000 Frames</span>Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4541271552202931674.post-70942701514301260192016-04-30T17:43:00.000+01:002016-05-02T15:24:51.250+01:00Sun, Full Disk Ha - 30-04-2016<span style="font-family: "arial" , "helvetica" , sans-serif;">Sun, Full Disk Hydrogen Alpha. (click images for full size). A couple of interesting plages today - the white areas to the lower centre and at the 8-O'Clock position.</span><br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEix9H-rhMuJT7bNYQlqwwZxsViAUq5e2fv30bw82qeCXMoxcuwls0C1xKgADySnKBoTCHleXhMICWivdFaS6GjC_iGJRbL65fLnee89ITHx2BigepwqpIf-ikF04NhFE9vfkgW5tfZ6rWg/s1600/Sun_Full_16_04_30_08_30_19_g3_ap2250_Blend_Final.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="632" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEix9H-rhMuJT7bNYQlqwwZxsViAUq5e2fv30bw82qeCXMoxcuwls0C1xKgADySnKBoTCHleXhMICWivdFaS6GjC_iGJRbL65fLnee89ITHx2BigepwqpIf-ikF04NhFE9vfkgW5tfZ6rWg/s640/Sun_Full_16_04_30_08_30_19_g3_ap2250_Blend_Final.png" width="640" /></a></div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjiih0OyXLjnt7Ur_c_OTzifENu1k1iRvYYjrI9Pz6uwV_2gUnxb-n3gIox__BPDC7Up6lFZq4C48Bfcf4Sc-QqEAIjvB3-4wuE6LCTZQA6ZeWW6Vdhyphenhypheno9fBh88LzhZbYSfRsx8pxKY5OM/s1600/Sun_Full_16_04_30_08_30_19_g3_ap2250_Blend_Inv_Final.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="632" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjiih0OyXLjnt7Ur_c_OTzifENu1k1iRvYYjrI9Pz6uwV_2gUnxb-n3gIox__BPDC7Up6lFZq4C48Bfcf4Sc-QqEAIjvB3-4wuE6LCTZQA6ZeWW6Vdhyphenhypheno9fBh88LzhZbYSfRsx8pxKY5OM/s640/Sun_Full_16_04_30_08_30_19_g3_ap2250_Blend_Inv_Final.png" width="640" /></a></div>
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b style="font-family: arial, helvetica, sans-serif;"><span style="color: orange;">Scope:</span></b><span style="font-family: "arial" , "helvetica" , sans-serif;"> </span><span style="font-family: "arial" , "helvetica" , sans-serif;">Lunt LS60THa/B1200CPT</span></span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><span style="color: orange;"><b>Camera:</b></span> ZWO ASI174MM, FireCapture</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Mount</span></b>: Sky-Watcher NEQ6, EQMod</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Processing:</span></b> AutoStakkert! 2, PixInsight 1.8, Gimp 2.8</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Date:</span></b> 30th April 2016, 08:30BST (07:30UT)</span><br />
<b style="font-family: arial, helvetica, sans-serif;"><span style="color: orange;">Frames:</span></b><span style="font-family: "arial" , "helvetica" , sans-serif;"> Best 25% of 1,000 Frames</span><span style="font-family: "arial" , "helvetica" , sans-serif;"></span>Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4541271552202931674.post-83582764811663640012016-04-24T19:00:00.001+01:002016-04-25T19:34:07.872+01:00DIY Laptop Shade / Dew Shield<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEha0FmyNWyDm9hFWBVRy1dhmpVASs8LKJIvw27-ymIrEnqYhR0IYozxgl9oIex7dVZhMfUstDYXY5RU-Xvm4BKHmPNfuskOSRPbWnqTQHNyeAJIYNrhLMGkYdF977GPFX631dg4AJDJA5k/s1600/IMG_20160424_163049.jpg" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"><img border="0" height="200" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEha0FmyNWyDm9hFWBVRy1dhmpVASs8LKJIvw27-ymIrEnqYhR0IYozxgl9oIex7dVZhMfUstDYXY5RU-Xvm4BKHmPNfuskOSRPbWnqTQHNyeAJIYNrhLMGkYdF977GPFX631dg4AJDJA5k/s200/IMG_20160424_163049.jpg" width="150" /></a><span style="font-family: "arial" , "helvetica" , sans-serif;">In this post, I will explain how to build a dual-purpose laptop shade / dew shield for a cost of approximately £20 (GBP). As explained in <a href="http://www.blackwaterskies.co.uk/2013/05/dew-formation-and-prevention.html">Dew Formation and Prevention</a>, the simplest way to prevent dew forming on equipment is to shield it from direct exposure to the night sky.</span><br />
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<span style="font-family: "arial" , "helvetica" , sans-serif;">Using this shield will help to extend the life of your equipment and avoid invalidating the warranty, though to be honest I've used my trusty laptop for years without a shield and it is still going strong. This shield is also helpful for solar imaging, making it much easier to see the screen in bright sunlight. </span><span style="font-family: "arial" , "helvetica" , sans-serif;">Read on for full instructions and plans.</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"></span><br />
<a name='more'></a><span style="font-family: "arial" , "helvetica" , sans-serif;">The exact size of laptop shield you require will of course depend on the size of your laptop, but the plans presented here will accommodate a large laptop quite comfortably. If you have a small laptop, you may be able to save on materials by scaling things down, but don't forget to allow room for cables and connectors around the edges of the laptop and also leave sufficient space for your head and arms.</span><br />
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<span style="font-family: "arial" , "helvetica" , sans-serif;">Materials</span></h3>
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<span style="font-family: "arial" , "helvetica" , sans-serif;">You will require the following materials for this build:</span></div>
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<li><span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Black Correx sheet:</span></b> I have based my design on 4 x A1 sheets (594 x 891mm each). These cost approximately £4.20 (GBP) each, and can be obtained from Amazon or eB</span><span style="font-family: "arial" , "helvetica" , sans-serif;">ay in a variety of sizes. Correx is a lightweight, waterproof and strong plastic sheet, commonly used for making signs and models.</span></li>
<li><span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Hot Glue:</span></b> The high temperature variety of hot glue is effective for joining the various seams in this build and takes a few moments to set hard, giving you time to align the joints. If you don't have a hot glue gun, then "Super Glue" (cyanoacrylate) is reported to be quite effective on Correx, but be aware that you will need reasonably large quantities for this build, and it sticks almost instantly. Test your glue on an offcut before proceeding.</span></li>
<li><span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Methylated Spirit:</span></b> You you will need some form of solvent to remove grease and manufacturing residue from the surface of the Correx prior to gluing the joints. I found methylated spirit worked fine, but test whatever you plan to use to ensure it doesn't dissolve the sheet.</span></li>
<li><span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Paper Towels:</span></b> Paper towels will be needed for the cleaning process.</span></li>
<li><span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Duck Tape:</span></b> A roll of Duck Tape will be needed to strengthen the joints.</span></li>
<li><span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Stanley Knife:</span></b> A fresh blade is essential for clean cuts.</span></li>
<li><span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Scissors:</span></b> A large, sharp pair of craft scissors is useful for cutting tape and scoring the Correx.</span></li>
<li><span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Large Steel Ruler:</span></b> A large straight edge will be needed to mark out the cuts and help when making them.</span></li>
<li><span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Cutting Surface:</span></b> I used a few sheets of corrugated cardboard as my cutting surface. Don't undertake this project on the best dining room table, but equally don't use a rough/uneven surface which will damage the Correx.</span></li>
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<span style="font-family: "arial" , "helvetica" , sans-serif;">Plans</span></h3>
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<div>
<span style="font-family: "arial" , "helvetica" , sans-serif;">The plan for this build is shown below:</span></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEivcNT2u6ExKYSPYhS0Q4gsUYDV8bRTBOPTXnYMOlidVLn9bSs-p05yRYtSuUD6Fx8xtF-UXnlKd80YP7EVgn_MsNfiLcyViriAE_z53i8dIaACaYAG65ytYF4gvaxYyL4EALP7s9qnTg4/s1600/Laptop+Shade.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="452" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEivcNT2u6ExKYSPYhS0Q4gsUYDV8bRTBOPTXnYMOlidVLn9bSs-p05yRYtSuUD6Fx8xtF-UXnlKd80YP7EVgn_MsNfiLcyViriAE_z53i8dIaACaYAG65ytYF4gvaxYyL4EALP7s9qnTg4/s640/Laptop+Shade.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="color: orange; font-family: "arial" , "helvetica" , sans-serif; font-size: small;">Laptop Shield Plan</span></td></tr>
</tbody></table>
<div>
<span style="font-family: "arial" , "helvetica" , sans-serif;">The plans can also be downloaded <a href="https://drive.google.com/file/d/0B1Thwu5Ko_kLbDZiTXRNclcwaFk/view?usp=sharing" target="_blank">here (PDF format) </a>or <a href="https://drive.google.com/file/d/0B1Thwu5Ko_kLTTdzbThBdzhBSEU/view?usp=sharing" target="_blank">here (Microsoft Visio 2016 format)</a>.</span></div>
<h3>
<span style="font-family: "arial" , "helvetica" , sans-serif;"><br /></span></h3>
<h3>
<span style="font-family: "arial" , "helvetica" , sans-serif;">Cutting and Folding</span></h3>
<div>
<span style="font-family: "arial" , "helvetica" , sans-serif;"><br /></span></div>
<div>
<span style="font-family: "arial" , "helvetica" , sans-serif;">Mark out each piece using the ruler and a ballpoint pen (black ink will show up reasonably well on the black Correx surprisingly enough). Measure twice and cut once; note that parts A and B and D and F are mirror images of each other so once you have cut the first, you can use it as a template to mark out the second piece more quickly.</span></div>
<div>
<span style="font-family: "arial" , "helvetica" , sans-serif;"><br /></span></div>
<div>
<span style="font-family: "arial" , "helvetica" , sans-serif;">When cutting the Correx, use the ruler to guide your knife, applying a firm downward pressure to avoid it slipping. Make a first shallow cut, then a second firm cut all the way through the sheet for best results. The Correx will withstand the weight of your hand easily, but don't kneel or stand on it otherwise you will crush it.</span></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgTI5daIaSlX9uIyeYrp_xcYMqWPJpcSdKr14ihALqU_wpOX6J_nJPG3TSm0KlKb2NV3xUP8bTqj13fvdu3jbh4n0VzOWHxSgda3DnVmhqgr1_xvCtt9bvQTJu-D9H_6OAxWcgjEd9rnqs/s1600/IMG_20160424_130943.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="480" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgTI5daIaSlX9uIyeYrp_xcYMqWPJpcSdKr14ihALqU_wpOX6J_nJPG3TSm0KlKb2NV3xUP8bTqj13fvdu3jbh4n0VzOWHxSgda3DnVmhqgr1_xvCtt9bvQTJu-D9H_6OAxWcgjEd9rnqs/s640/IMG_20160424_130943.jpg" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="color: orange; font-family: "arial" , "helvetica" , sans-serif; font-size: small;">Cut Pieces Ready for Assembly</span></td></tr>
</tbody></table>
<div>
<span style="font-family: "arial" , "helvetica" , sans-serif;">Score along the dotted red lines where shown on the plans. Use the ruler and the back (blunt) side of the scissors firmly to make a deep impression in the sheet, but don't cut in to the surface with a sharp edge. Note that the scoring should be on the top side of each sheet as shown in the plans.</span></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhSlQ1Xg18HX4QTkdQp1UVMDHqY7s-Faq1C8Hc4wd24NUTdqM3q3wENavxP9_WBnS59drvbdtiM2gMsqVNpqeyl0XGTymPbhi8IbA0jvLu84tDBb_oELP8m6IwNAnnq7HbZNoOHGyqaANg/s1600/IMG_20160424_142350.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="480" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhSlQ1Xg18HX4QTkdQp1UVMDHqY7s-Faq1C8Hc4wd24NUTdqM3q3wENavxP9_WBnS59drvbdtiM2gMsqVNpqeyl0XGTymPbhi8IbA0jvLu84tDBb_oELP8m6IwNAnnq7HbZNoOHGyqaANg/s640/IMG_20160424_142350.jpg" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="color: orange; font-family: "arial" , "helvetica" , sans-serif; font-size: small;">Scored and Folded Edge</span></td></tr>
</tbody></table>
<div>
<span style="font-family: "arial" , "helvetica" , sans-serif;">Start folding the scored edge upwards (towards you as shown on the plan). Grasp the rear of the tab with your fingers and press down on the front of the sheet with your thumbs and fold gently, working your way along the scored line. You should find that the sheet folds readily and you will end up with a straight fold. Bend the tab right over flat to the surface of the sheet; it will spring back, but that's fine for now.</span></div>
<h3>
<span style="font-family: "arial" , "helvetica" , sans-serif;"><br /></span></h3>
<h3>
<span style="font-family: "arial" , "helvetica" , sans-serif;">Initial Assembly</span></h3>
<div>
<span style="font-family: "arial" , "helvetica" , sans-serif;"><br /></span></div>
<div>
<span style="font-family: "arial" , "helvetica" , sans-serif;">Assemble the shade in the following order:</span></div>
<div>
<ul>
<li><span style="font-family: "arial" , "helvetica" , sans-serif;">Place part E on top of part C, so that E folds up towards you. Tape and glue as explained below and then proceed to the next part.</span></li>
<li><span style="font-family: "arial" , "helvetica" , sans-serif;">Parts D and F are placed on top of E, again so that they fold towards you.</span></li>
<li><span style="font-family: "arial" , "helvetica" , sans-serif;">Parts A and B are placed on top of Part C, again folding up towards you.</span></li>
</ul>
</div>
<div>
<span style="font-family: "arial" , "helvetica" , sans-serif;">The first seam is assembled as follows:</span></div>
<div>
<ul>
<li><span style="font-family: "arial" , "helvetica" , sans-serif;">Step one is to lay part E on top of part C, so that E folds up towards you. Align the parts as shown in the assembly diagram. Now turn over the two pieces together so that the underside of the seam is facing you (the tab of part E should now be <u>underneath</u> part C). Clean along both sides of the seam facing you using a paper towel and some solvent. This will remove any grease or other residue and ensure you have a good bond. Take care to ventilate your working area as set out on the solvent's instructions.</span></li>
</ul>
<ul><table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhLzx9i3oC1-FJgGl13ospmD6OAl5YGckQPldES_07z_JdJsIWjYqt-TKipkAMvavE6eHGQFOfTGfan0mDTTo6enqmAdU1lxEuyTrYwYgHlFT2zOWCKG9su39-u97CvZQkL6gLW6cAWR_g/s1600/IMG_20160424_142951.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="300" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhLzx9i3oC1-FJgGl13ospmD6OAl5YGckQPldES_07z_JdJsIWjYqt-TKipkAMvavE6eHGQFOfTGfan0mDTTo6enqmAdU1lxEuyTrYwYgHlFT2zOWCKG9su39-u97CvZQkL6gLW6cAWR_g/s400/IMG_20160424_142951.jpg" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="color: orange; font-family: "arial" , "helvetica" , sans-serif; font-size: small;">Tape the Bottom Side of the Seam</span></td></tr>
</tbody></table>
<li><span style="font-family: "arial" , "helvetica" , sans-serif;">Step two is to take a length of Duck Tape and stick along the seam. Take your time to keep the edges of the seam aligned and press the tape down firmly, removing any air bubbles or creases. If you get it wrong the tape will peel off easily and you can try again.</span></li>
</ul>
</div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgQHi84tmHpgrb7CIJZkO5VsfOWhRC0k_BdLEOsgwjK3ZXsxb-tcpqotesnHp8NAIlT8RkvA2HfRX8w-M68nG8JHc1sIVnJn18h8yMRgj0OFXWBRmAX_dTWgxJLdDE86xTyYxQyT1iEeAE/s1600/IMG_20160424_143030.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgQHi84tmHpgrb7CIJZkO5VsfOWhRC0k_BdLEOsgwjK3ZXsxb-tcpqotesnHp8NAIlT8RkvA2HfRX8w-M68nG8JHc1sIVnJn18h8yMRgj0OFXWBRmAX_dTWgxJLdDE86xTyYxQyT1iEeAE/s400/IMG_20160424_143030.jpg" width="300" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="color: orange; font-family: "arial" , "helvetica" , sans-serif; font-size: small;">Fold Parts Together and Turn Over</span></td></tr>
</tbody></table>
<div>
<ul>
<li><span style="font-family: "arial" , "helvetica" , sans-serif;">Step three is to fold together the two pieces using the Duck Tape as a "hinge". Now turn them over again so the top side of part C facing you with the tab of part E protruding from underneath it. Clean the tab and the adjoining surface of part C.</span></li>
</ul>
</div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiEl2mc93jPimleiz3cB7JaZa5bwGs3XLXJ2LEFnFackLjHiur8lWS3MT0JQtv5ZutESXqTVB0ye3o50yPLq7a4w0JDRgfYbsG0uqKGeSoVQ4iAMQDaasbGR5rWUQHEwsumUz587obrkpI/s1600/IMG_20160424_143202.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiEl2mc93jPimleiz3cB7JaZa5bwGs3XLXJ2LEFnFackLjHiur8lWS3MT0JQtv5ZutESXqTVB0ye3o50yPLq7a4w0JDRgfYbsG0uqKGeSoVQ4iAMQDaasbGR5rWUQHEwsumUz587obrkpI/s400/IMG_20160424_143202.jpg" width="300" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="color: orange; font-family: "arial" , "helvetica" , sans-serif; font-size: small;">Glue Tab and Fold Back</span></td></tr>
</tbody></table>
<div>
<div class="separator" style="clear: both; text-align: center;">
</div>
<ul>
<li><span style="font-family: "arial" , "helvetica" , sans-serif;">Step four is to apply glue along the whole length of the tab and then flip part E out from under part C using the Duck Tape "hinge". Press the glued surface of the tab on to the top of part C; the Duck Tape should ensure that the two pieces align properly but adjust so that the scored seam on part E aligns with the corresponding edge of part C before the glue hardens.</span></li>
</ul>
</div>
<div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgvI-WZnGFArNFnG6B9lYoj5WMf2nBQX9nQSWgQuposbxAXGlJvixh2KkVWjQ_WOiVeNWgAXAuh8Kweh1Hfbmww_Ud0aevI1TFRZO3zXoD8S71pD5HSmDPBvQc66OiaY57XW-h0VJMc3yc/s1600/IMG_20160424_143552.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgvI-WZnGFArNFnG6B9lYoj5WMf2nBQX9nQSWgQuposbxAXGlJvixh2KkVWjQ_WOiVeNWgAXAuh8Kweh1Hfbmww_Ud0aevI1TFRZO3zXoD8S71pD5HSmDPBvQc66OiaY57XW-h0VJMc3yc/s400/IMG_20160424_143552.jpg" width="300" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="color: orange; font-family: "arial" , "helvetica" , sans-serif; font-size: small;">Clean and Tape the Seam</span></td></tr>
</tbody></table>
<ul>
<li><span style="font-family: "arial" , "helvetica" , sans-serif;">Step five is to clean and then tape the top side of the seam as you did for the bottom side.</span></li>
</ul>
</div>
<div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjWgK5VdrhcPGU_q9QdBjXIgcEP_ykgaWJnb8foYmnXdEqXNG3k1GbpG701RhvZggOSxlDKnIP5D61y_HAaJQ8fs2QFHTANSI3nOV06o8KOinPIUQKamxWADKOw_UzRqw7tGJBleI3cTA8/s1600/IMG_20160424_153255.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjWgK5VdrhcPGU_q9QdBjXIgcEP_ykgaWJnb8foYmnXdEqXNG3k1GbpG701RhvZggOSxlDKnIP5D61y_HAaJQ8fs2QFHTANSI3nOV06o8KOinPIUQKamxWADKOw_UzRqw7tGJBleI3cTA8/s400/IMG_20160424_153255.jpg" width="300" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="color: orange; font-family: "arial" , "helvetica" , sans-serif; font-size: small;">All Parts Assembled</span></td></tr>
</tbody></table>
<ul>
<li><span style="font-family: "arial" , "helvetica" , sans-serif;">Assemble the other parts in exactly the same manner, in the order set out above. You should end up with a flat assembly as shown above.</span></li>
</ul>
</div>
<h3>
<span style="font-family: "arial" , "helvetica" , sans-serif;"><br /></span></h3>
<h3>
<span style="font-family: "arial" , "helvetica" , sans-serif;">Final Assembly</span></h3>
<div>
<span style="font-family: "arial" , "helvetica" , sans-serif;"><br /></span></div>
<div>
<span style="font-family: "arial" , "helvetica" , sans-serif;">The last part of the process is to fold and stick the flat assembly in to the 3D shape of the laptop shade as follows:</span></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjmbl99rwjVJDqrEl8G7LfNGBh9ZpsEL8Geb6o2WZSKOJ-42ZVTteadgIP1pIEuk_kZNQN5kFOhWTp1uZOlqaaIZ8EnLy_zBaGLq8i1LOSdBwajJQhwfI8Lc8qzIiOwphO_QLn38j1nuhs/s1600/IMG_20160424_153900.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjmbl99rwjVJDqrEl8G7LfNGBh9ZpsEL8Geb6o2WZSKOJ-42ZVTteadgIP1pIEuk_kZNQN5kFOhWTp1uZOlqaaIZ8EnLy_zBaGLq8i1LOSdBwajJQhwfI8Lc8qzIiOwphO_QLn38j1nuhs/s400/IMG_20160424_153900.jpg" width="300" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="color: orange; font-family: "arial" , "helvetica" , sans-serif; font-size: small;">Joining A and D</span></td></tr>
</tbody></table>
<div>
<ul>
<li><span style="font-family: "arial" , "helvetica" , sans-serif;">Step one is to fold the scored seams between A-C, C-E and D-E together to create one side of the shade. You are aiming to align the black dotted line of part A (as shown on the plan) with the adjacent edge of part D. Note that A should end up underneath D. The scored folds in the Correx will be quite springy and the whole assembly will want to fly apart, so an extra pair of hands may be needed.</span></li>
<li><span style="font-family: "arial" , "helvetica" , sans-serif;">Step two is to hold the joint between A and D temporarily using a scrap of tape or through the aid of your assistant. Mark the edge of part D on to part A using a ballpoint pen. Now release the joint and clean the two facing surfaces to be joined.</span></li>
<li><span style="font-family: "arial" , "helvetica" , sans-serif;">Step three is to apply hot glue along the edge of part A and then re-fold the shield together, aligning parts A and D along the line you marked in step two. Work quickly before the glue sets and then hold the parts together until the joint is secure.</span></li>
<li><span style="font-family: "arial" , "helvetica" , sans-serif;">Step four is to clean and tape both sides of this joint as you did for previous joints.</span></li>
</ul>
</div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh5gj8MMAXfc60FTp9UrjRR5isdRE7PRHcU6waKenr-fUyHFQUWFc-okqvECEUh6DSKtHYkhNkNCIgT7vS7sCF_fQsb5D1VpD_XGBQ0mcbNCd5U8Wf24XASt8YxPAOaMrVoAMfwsSar6G8/s1600/IMG_20160424_162121.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="480" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh5gj8MMAXfc60FTp9UrjRR5isdRE7PRHcU6waKenr-fUyHFQUWFc-okqvECEUh6DSKtHYkhNkNCIgT7vS7sCF_fQsb5D1VpD_XGBQ0mcbNCd5U8Wf24XASt8YxPAOaMrVoAMfwsSar6G8/s640/IMG_20160424_162121.jpg" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="color: orange; font-family: "arial" , "helvetica" , sans-serif; font-size: small;">The Completed Shade</span></td></tr>
</tbody></table>
<div>
<ul>
<li><span style="font-family: "arial" , "helvetica" , sans-serif;">Repeat steps one through four for the other side of the shade so that you join parts B and F in the same manner.</span></li>
<li><span style="font-family: "arial" , "helvetica" , sans-serif;">Finally take part G and glue/tape it to the bottom front edge of the shade as shown above. Note that I have used a thin strip for part G as I want to place this shade on top of a tool chest that holds my laptop. If you wish, you could make part G from an extra sheet of Correx to make a solid base for the shade, e.g. if your laptop sits on a table.</span></li>
<li><span style="font-family: "arial" , "helvetica" , sans-serif;">You may also want to chamfer the corners of the front/top of the shade as shown in the photographs to avoid them getting bent or poking you in the eye.</span></li>
</ul>
<span style="font-family: "arial" , "helvetica" , sans-serif;">Below you can see that the completed shade sits on top of my tool chest, which has a shelf mounted in it for the laptop. The laptop screen can be angled back for best viewing according to whether you are sitting or standing and to reduce any remaining reflections from behind you:</span></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjphxI9CgKO5F49zIRF6ztbBK2JUVQg1t8tfMs_5DChx40Z7VRdC8x_lO7bSpEAeYKaQmSwrvUN8FuXD9vEi3dDTxJlfd6_JLre8n9zRFiCZusTo_jr0aO3JufLNm6-ulTjASiwQuqPxAk/s1600/IMG_20160424_163049.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjphxI9CgKO5F49zIRF6ztbBK2JUVQg1t8tfMs_5DChx40Z7VRdC8x_lO7bSpEAeYKaQmSwrvUN8FuXD9vEi3dDTxJlfd6_JLre8n9zRFiCZusTo_jr0aO3JufLNm6-ulTjASiwQuqPxAk/s640/IMG_20160424_163049.jpg" width="480" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="color: orange; font-family: "arial" , "helvetica" , sans-serif; font-size: small;">The Completed Shade in Action</span></td></tr>
</tbody></table>
<div>
<span style="font-family: "arial" , "helvetica" , sans-serif;"><br /></span></div>
Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4541271552202931674.post-62132143443666265412016-04-17T18:19:00.002+01:002016-09-29T11:06:37.639+01:00Sunspot Animation (AR2529) in Ha 17th April 2016<div class="separator" style="clear: both; text-align: left;">
<span style="font-family: "arial" , "helvetica" , sans-serif;">A week on, AR2529 is still going strong, but about to disappear behind the solar limb. (Click image for full-sized version).</span></div>
<div class="separator" style="clear: both; text-align: left;">
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiaAlZFNv937VC6EaexgXB9S8x1qeT_gvrMyhtoGMe11XwC6dePn2cxznl9xv6tdNSip9g3h5tiWPcGeIe5f6XDJYHPk_VTfitmP_nZ719GNYu4aachN_B9sR7oD1O0ypVaLhaD3Zugz4Y/s1600/Anim.gif" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiaAlZFNv937VC6EaexgXB9S8x1qeT_gvrMyhtoGMe11XwC6dePn2cxznl9xv6tdNSip9g3h5tiWPcGeIe5f6XDJYHPk_VTfitmP_nZ719GNYu4aachN_B9sR7oD1O0ypVaLhaD3Zugz4Y/s640/Anim.gif" width="632" /></a></div>
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<b style="font-family: arial, helvetica, sans-serif;"><span style="color: orange;">Scope:</span></b><span style="font-family: "arial" , "helvetica" , sans-serif;"> </span><span style="font-family: "arial" , "helvetica" , sans-serif;">Lunt LS60THa/B1200CPT, Meade 2x Barlow</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><span style="color: orange;"><b>Camera:</b></span> ZWO ASI174MM, FireCapture</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Mount</span></b>: Sky-Watcher NEQ6, EQMod</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Processing:</span></b> AutoStakkert! 2, IMPPG, PixInsight 1.8, Gimp 2.8</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Date:</span></b> 17th April 2016</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Frames:</span></b> Best 25% of 500 Frames, 30 seond intervals</span>Unknownnoreply@blogger.com1tag:blogger.com,1999:blog-4541271552202931674.post-71388404705770417712016-04-17T15:36:00.001+01:002016-04-24T17:08:40.812+01:00Full Disk Ha 17 April 2016<div class="separator" style="clear: both; text-align: left;">
<span style="font-family: "arial" , "helvetica" , sans-serif;">Sun, Full Disk Hydrogen Alpha. (click images for full size).</span></div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjqwJ0FpaYHiUnik1d_g7nXQJcnpMFZTUjwEjkSWTFHrG6WUP5aYoprncQPz2Go_QHzIeeB_dis11aSh0XPXU84DqfTxK6VaRluObR0RYB5BzIBc1zbZIbQP2eYS-dc6yaGtqfaQ7yylv8/s1600/Sun_Full_16_04_17_08_44_08_g3_ap2308_Drizzle15_Final_Labelled.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="620" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjqwJ0FpaYHiUnik1d_g7nXQJcnpMFZTUjwEjkSWTFHrG6WUP5aYoprncQPz2Go_QHzIeeB_dis11aSh0XPXU84DqfTxK6VaRluObR0RYB5BzIBc1zbZIbQP2eYS-dc6yaGtqfaQ7yylv8/s640/Sun_Full_16_04_17_08_44_08_g3_ap2308_Drizzle15_Final_Labelled.png" width="640" /></a></div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjVJS75IT2pz3n16CQ_Y3CSKZzCH9atQsJA96mRr5vmTWfJo84MeG3R5QQMAhT6B3lGlUEQtlWZPQQ0atLEw8Trqfmn8wZlEtyCVknAuo9KQHT4ak5KnIOcCIPyfiSt_82KnKzdy0ES0Xg/s1600/Sun_Full_16_04_17_08_44_08_g3_ap2308_Drizzle15_Invert_Final_Labelled.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="620" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjVJS75IT2pz3n16CQ_Y3CSKZzCH9atQsJA96mRr5vmTWfJo84MeG3R5QQMAhT6B3lGlUEQtlWZPQQ0atLEw8Trqfmn8wZlEtyCVknAuo9KQHT4ak5KnIOcCIPyfiSt_82KnKzdy0ES0Xg/s640/Sun_Full_16_04_17_08_44_08_g3_ap2308_Drizzle15_Invert_Final_Labelled.png" width="640" /></a></div>
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<b style="font-family: arial, helvetica, sans-serif;"><span style="color: orange;">Scope:</span></b><span style="font-family: "arial" , "helvetica" , sans-serif;"> </span><span style="font-family: "arial" , "helvetica" , sans-serif;">Lunt LS60THa/B1200CPT</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><span style="color: orange;"><b>Camera:</b></span> ZWO ASI174MM, FireCapture</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Mount</span></b>: Sky-Watcher NEQ6, EQMod</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Processing:</span></b> AutoStakkert! 2, PixInsight 1.8, Gimp 2.8</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Date:</span></b> 17th April 2016, 08:44BST (07:44UT)</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Frames:</span></b> Best 10% of 1,000 Frames</span>Unknownnoreply@blogger.com1tag:blogger.com,1999:blog-4541271552202931674.post-79010218865741572302016-04-10T22:29:00.001+01:002016-09-29T11:07:00.741+01:00Large Sunspot Animation (AR2529) in Ha 10-04-2016<span style="font-family: "arial" , "helvetica" , sans-serif;">Another animation of AR2529 (a sunspot), taken in Hydrogen Alpha. This is a different set of images from the previous post and shown in the normal (not inverted) colour scheme. Click the image below for the full-sized view (you might have to wait a few moments for it to load).</span><br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhKYVFQyJq6A65HG1Ws1WSl3685ZW4FBn5L7Xpk8T-3yTzb8M3m_GMKl_y-R_aDGK_TXwYAX4EW7hdBvJIZeWQLRsRJeMuBIRVHL4sU6SHL7ggDe50tce2kUt5O7XKIXBm2_ATMcwDVURM/s1600/AR2529_Large.gif" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" height="547" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhKYVFQyJq6A65HG1Ws1WSl3685ZW4FBn5L7Xpk8T-3yTzb8M3m_GMKl_y-R_aDGK_TXwYAX4EW7hdBvJIZeWQLRsRJeMuBIRVHL4sU6SHL7ggDe50tce2kUt5O7XKIXBm2_ATMcwDVURM/s640/AR2529_Large.gif" width="640" /></a></div>
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<b style="font-family: arial, helvetica, sans-serif;"><span style="color: orange;">Scope:</span></b><span style="font-family: "arial" , "helvetica" , sans-serif;"> </span><span style="font-family: "arial" , "helvetica" , sans-serif;">Lunt LS60THa/B1200CPT, Meade 2x Barlow</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><span style="color: orange;"><b>Camera:</b></span> ZWO ASI174MM, FireCapture</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Mount</span></b>: Sky-Watcher NEQ6, EQMod</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Processing:</span></b> AutoStakkert! 2, IMPPG, PixInsight 1.8, Gimp 2.8</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Date:</span></b> 3rd April 2016</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Frames:</span></b> Best 50% of 500 Frames, 30 seond intervals</span>Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4541271552202931674.post-20331542738423530232016-04-10T17:04:00.002+01:002016-09-29T11:07:42.470+01:00Sunspot Animation (AR2529) in Ha 10-04-2016<span style="font-family: "arial" , "helvetica" , sans-serif;">Animation of AR2529 (a sunspot), taken in Hydrogen Alpha. The image is inverted so the sunspot appears white against a dark background, as this allows much more of the image detail to be seen.</span><br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiMO-rOnisAPu2iDrAeBQMidSs8HGWzANeQshkic5qK-ukiW097K3zWdpKL91ZnxTi45AJENCsVndx8bagtGBTHmrFvf0gwoPPK4Y_XZL-RF3fRf-_iAo4Rj7fs8Kk1QePCTmKTMoZ1s2k/s1600/AR2529_Small.gif" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" height="612" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiMO-rOnisAPu2iDrAeBQMidSs8HGWzANeQshkic5qK-ukiW097K3zWdpKL91ZnxTi45AJENCsVndx8bagtGBTHmrFvf0gwoPPK4Y_XZL-RF3fRf-_iAo4Rj7fs8Kk1QePCTmKTMoZ1s2k/s640/AR2529_Small.gif" width="640" /></a></div>
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<b style="font-family: arial, helvetica, sans-serif;"><span style="color: orange;">Scope:</span></b><span style="font-family: "arial" , "helvetica" , sans-serif;"> </span><span style="font-family: "arial" , "helvetica" , sans-serif;">Lunt LS60THa/B1200CPT, Meade 2x Barlow</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><span style="color: orange;"><b>Camera:</b></span> ZWO ASI174MM, FireCapture</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Mount</span></b>: Sky-Watcher NEQ6, EQMod</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Processing:</span></b> AutoStakkert! 2, IMPPG, PixInsight 1.8, Gimp 2.8</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Date:</span></b> 3rd April 2016</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Frames:</span></b> Best 50% of 500 Frames, 30 seond intervals</span>Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4541271552202931674.post-33549219940988505572016-04-09T16:20:00.001+01:002016-09-29T11:07:59.484+01:00Solar Prominence Animation in Ha, 3rd April 2016<span style="font-family: "arial" , "helvetica" , sans-serif;">A solar prominence animation in Hydrogen Alpha (with the Earth shown approximately to scale). This is my first attempt, as a bit challenging to create as there were a lot of high clouds drifting through. This has created some long gaps between frames and a few odd artefacts around the prominences and disk where I had to try to get an even sky background. Nonetheless you can clearly see the rotation of the solar disk and rapid changes in the prominences over a period of about two hours and forty minutes.</span><br />
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<span style="font-family: "arial" , "helvetica" , sans-serif;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhxylxi2_ixZx1cLDfodG-1CGy8gTF_lc_rbaf0WSmtUw21zZAiVZKSLE0G3BXPgSE7Br3MMQrd2ilXp6hb8ckcS7jNTtHV59W6JC0r2fnbYSVpcZOUoVrjX7PUHR7DiQSHig8mSZjpabU/s1600/03-04-16+Final.gif" imageanchor="1"><img border="0" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhxylxi2_ixZx1cLDfodG-1CGy8gTF_lc_rbaf0WSmtUw21zZAiVZKSLE0G3BXPgSE7Br3MMQrd2ilXp6hb8ckcS7jNTtHV59W6JC0r2fnbYSVpcZOUoVrjX7PUHR7DiQSHig8mSZjpabU/s640/03-04-16+Final.gif" width="540" /></a></span><br />
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<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Scope:</span></b> Lunt LS60THa/B1200CPT, Meade 2x Barlow</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><span style="color: orange;"><b>Camera:</b></span> ZWO ASI174MM, FireCapture</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Mount</span></b>: Sky-Watcher NEQ6, EQMod</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Processing:</span></b> AutoStakkert! 2, IMPPG, PixInsight 1.8, Gimp 2.8</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Date:</span></b> 3rd April 2016</span><br />
<span style="font-family: "arial" , "helvetica" , sans-serif;"><b><span style="color: orange;">Frames:</span></b> Best 10% of 1,000 Frames, 2 minute intervals</span>Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4541271552202931674.post-17031758091892605282015-02-19T13:42:00.000+00:002015-02-19T13:42:30.932+00:00PixInsight DSLR Workflow - Part 2a, Dark Frames<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiQZJc_JdFwpoi8AYXOKeyuQyTotu6jcHEQB_2nhoOVVIhDo-xtckTHJxZZ-K5dCeQgPKhpCTqlKKIpwqCBgvhQCFsH39dUqnGldda3Q5IBB6VjWMSS5hurpokIIsgQP-u87LPFKnMhMTY/s1600/median_temp_all.png" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiQZJc_JdFwpoi8AYXOKeyuQyTotu6jcHEQB_2nhoOVVIhDo-xtckTHJxZZ-K5dCeQgPKhpCTqlKKIpwqCBgvhQCFsH39dUqnGldda3Q5IBB6VjWMSS5hurpokIIsgQP-u87LPFKnMhMTY/s1600/median_temp_all.png" height="198" width="320" /></a><span style="font-family: Arial, Helvetica, sans-serif;">In this third post explaining my PixInsight workflow, we'll be taking a look at dealing with Dark Current by creating and applying dark frames using a Canon EOS 500D. I think it is fair to say that creating a good master dark in order to calibrate flat and light frames is one of the more challenging parts of the image acquisition process when using a DSLR. There are many mysteries, a fair few myths and indeed some question as to whether DSLR users should bother with dark frames at all.</span><br />
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<span style="font-family: Arial, Helvetica, sans-serif;">Firstly though, it is worth reminding ourselves of what "Dark Current" is. Camera sensors create an image by measuring </span><span style="font-family: Arial, Helvetica, sans-serif;">electrons that are displaced in to the sensor's electron wells as they gain energy from incoming photons of light. Unfortunately, those electrons can also gain energy from heat in the sensor. Some of this heat may be come from the local environment and some will be generated by the sensor electronics. This process occurs in all exposures, even if the sensor is completely shielded from external light, hence the name "Dark Current".</span><br />
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<span style="font-family: Arial, Helvetica, sans-serif;">Dark current increases both with the length of an exposure (as there is more time for it to accumulate) and with the temperature of the camera sensor (as there is more energy available to displace electrons). The net result is that all pixels in an image will get brighter over time and with increasing temperature. </span><span style="font-family: Arial, Helvetica, sans-serif;">In theory we can create a master dark frame to measure the dark current and quite literally subtract this extra brightness from the image, but the practice for DSLR imagers is somewhat more complicated. </span><br />
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<span style="font-family: Arial, Helvetica, sans-serif;">Read on to find out about my method of tackling the problem. </span><span style="font-family: Arial, Helvetica, sans-serif;">(If you've arrived part way through, start the series here with </span><a href="http://www.blackwaterskies.co.uk/2013/09/pixinsight-dslr-workflow-part-1-bias.html" style="font-family: Arial, Helvetica, sans-serif;">Bias Frames</a><span style="font-family: Arial, Helvetica, sans-serif;">).</span></div>
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<a name='more'></a><span style="color: orange; font-family: Arial, Helvetica, sans-serif;"><b>Purpose of Dark Frames</b></span><br />
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<span style="font-family: Arial, Helvetica, sans-serif;">If we had a perfect sensor that accumulated dark current in every sensor element at the same rate, then we would not need to bother with dark frame subtraction at all. It would be sufficient to move the black point of the image <a href="http://www.blackwaterskies.co.uk/2013/12/how-to-interpret-image-histogram.html">histogram</a> further to the right in order to subtract the same value from every pixel and thus eliminate the unwanted brightening of the image caused by the dark current.</span></div>
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<span style="font-family: Arial, Helvetica, sans-serif;">In the real world however, the majority of pixels will accumulate dark current at slightly differing rates. Furthermore, a few cold pixels will accumulate dark current much more slowly than the majority and a few hot pixels will accumulate it much more rapidly. </span><span style="font-family: Arial, Helvetica, sans-serif;">Thus each individual sub-exposure contains a fixed pattern of dark current which cannot be removed by manipulating histogram to subtract a single value from every pixel.</span></div>
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<b><span style="font-family: Arial, Helvetica, sans-serif;">So t</span><span style="font-family: Arial, Helvetica, sans-serif;">he first objective of calibration using a dark frame is to accurately reproduce the fixed pattern created by the dark current and subtract it from our image.</span></b></div>
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<span style="font-family: Arial, Helvetica, sans-serif;">The standard process when using a set-point cooled astronomical CCD is to cap the camera with a light-proof cover, cool it to the same temperature as used to take the light frames and shoot a series of dark frame exposures of the same length as the lights.</span><br />
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<span style="font-family: Arial, Helvetica, sans-serif;">Since no light has hit the camera's sensor, any values in the resulting dark frames must be there as a result of the dark current (plus the fixed pattern and read-out noise which we covered in </span><a href="http://www.blackwaterskies.co.uk/2013/09/pixinsight-dslr-workflow-part-1-bias.html" style="font-family: Arial, Helvetica, sans-serif;">Bias Frames</a>)<span style="font-family: Arial, Helvetica, sans-serif;">. By matching the sensor temperature and exposure length between dark frames and light frames, we can accurately measure the dark current and subtract it from the light frames, thus achieving our first objective.</span><br />
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<span style="font-family: Arial, Helvetica, sans-serif;"><b>Our second and equally important objective is to introduce the least amount of additional noise whilst performing dark frame calibration.</b></span><br />
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<span style="font-family: Arial, Helvetica, sans-serif;">Dark current accumulates in a statistically random manner which creates <span style="color: orange;">dark current noise</span>. Dark current noise increases in proportion to the square root of the dark current. Therefore one obvious way to minimise dark current noise is to minimise dark current itself!</span></div>
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<span style="font-family: Arial, Helvetica, sans-serif;">Again a cooled camera offers significant benefits in this regard; we know that lower temperatures bring less dark current and so there must also be correspondingly less dark current noise, i.e. half the dark current = a quarter of the dark current noise. Since w</span><span style="font-family: Arial, Helvetica, sans-serif;">e're talking about an uncooled DSLR that point may seem irrelevant, but I'll explain shortly why it does matter.</span></div>
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<b style="color: orange; font-family: Arial, Helvetica, sans-serif;">Note: If you have a cooled sensor and a good quality camera, the dark current might be sufficiently low that you can get away without using dark subtraction at all. Unfortunately this is usually not the case with unmodified DSLRs.</b></div>
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<span style="font-family: Arial, Helvetica, sans-serif;">The other means by which we can minimise the effect of dark current noise is to do exactly as we did when creating our bias frames. By taking a large number of dark frames and integrating (stacking) them in to a master dark we can improve its signal to noise ratio (<span style="color: orange;">SNR</span>). </span><span style="font-family: Arial, Helvetica, sans-serif;">In this case the "signal" is the fixed pattern element of the <span style="color: orange;">dark current</span> and the noise is <span style="color: orange;">dark current noise</span></span><span style="font-family: Arial, Helvetica, sans-serif;">. It is the ratio of dark current fixed pattern to dark current noise that we are interested in increasing.</span></div>
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<span style="font-family: Arial, Helvetica, sans-serif;">Integrating multiple dark frames in to a <span style="color: orange;">master dark</span> improves the SNR (<span style="color: orange;">ΔSNR</span>) for each additional frame stacked as</span><span style="font-family: Arial, Helvetica, sans-serif;"> <span style="color: orange;">ΔSNR = √ n - √ (n -1)</span></span><span style="font-family: Arial, Helvetica, sans-serif;"> where <span style="color: orange;">n</span> is the number of dark frames. </span><span style="font-family: Arial, Helvetica, sans-serif;">You will notice that this is the same relationship as in previous post on <a href="http://www.blackwaterskies.co.uk/2013/09/pixinsight-dslr-workflow-part-1-bias.html">Bias Frames</a>. (Note that this says nothing about the <u>absolute</u> SNR of a given master dark, simply how much better one master dark is <u>relative</u> to others built from fewer frames.)</span><br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgkatx7KYZxW0IMvOzsqo9rVNtVEUHJX8VqPmBrzpHv7DDvm5E0IGYCjIy94t9yTBHhoJaQHS4iplco9hFjc_tb49G3WCfqPp3ZuANb2BYidkdGP6j3fqMvL3ByDbjjXMVu5j8CgPaOyYI/s1600/snr+stacking.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgkatx7KYZxW0IMvOzsqo9rVNtVEUHJX8VqPmBrzpHv7DDvm5E0IGYCjIy94t9yTBHhoJaQHS4iplco9hFjc_tb49G3WCfqPp3ZuANb2BYidkdGP6j3fqMvL3ByDbjjXMVu5j8CgPaOyYI/s1600/snr+stacking.png" height="379" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="color: orange; font-family: Arial, Helvetica, sans-serif; font-size: small;">SNR Improvement as a Function of Total Dark Frames</span></td></tr>
</tbody></table>
<span style="font-family: Arial, Helvetica, sans-serif;">The conclusion is the same as for a bias frame; a master dark constructed from more dark frames has a better SNR, i.e. it better represents the true dark current. After a certain point the improvement is not worth the extra effort required. A stack of 100 frames has a SNR that is 10 times better than a single frame, but to make it 20 times better you would have to stack 400 frames, 30 times better needs 900 frames and so on.</span><br />
<br />
<span style="font-family: Arial, Helvetica, sans-serif;">In <u>absolute</u> terms, if we start with less noisy dark frames we can stack fewer of them to reach the same SNR compared with stacking noisier dark frames. <b>For DSLR users, that means the higher the temperature of the dark frames, the more of them we are going to need, so anything you can do to keep the camera cool should make life easier for you.</b></span><br />
<br />
<span style="font-family: Arial, Helvetica, sans-serif;">Okay so that's the theory but unlike bias frames, for DSLR users there are some practical problems which make it much harder to create a sufficiently large stack of darks.</span></div>
<span style="font-family: Arial, Helvetica, sans-serif;"></span><br />
<div>
<span style="color: orange; font-family: Arial, Helvetica, sans-serif;"><b>Taking Dark Frames</b></span></div>
<span style="font-family: Arial, Helvetica, sans-serif;"></span><br />
<div>
<span style="font-family: Arial, Helvetica, sans-serif;">The first of those problems is the need to create lots of dark frames with similar temperatures. I needed a reasonably large set of matching darks </span><span style="font-family: Arial, Helvetica, sans-serif;">for the various experiments that I had in mind. </span><span style="font-family: Arial, Helvetica, sans-serif;">As previously noted, this is easier said than done due to the lack of cooling on a DSLR.</span></div>
<span style="font-family: Arial, Helvetica, sans-serif;"></span><br />
<div>
<span style="font-family: Arial, Helvetica, sans-serif;">The method I used was as follows:</span></div>
<ul>
<li><span style="font-family: Arial, Helvetica, sans-serif;">Firstly I needed to make sure no light could get in to the camera as I planned to take the darks during the day when I had time available. It is worth noting that light can leak in to the camera through the viewfinder or even gaps in the body, and also that many plastic lens/camera caps transmit a fair amount of infra-red light (some of which will be detected by the sensor despite the IR blocking filter in a standard Canon DSLR).</span></li>
<li><span style="font-family: Arial, Helvetica, sans-serif;">I also needed to cool the camera to something approaching the temperatures in which I had been imaging. At the time of my experiments, I was imaging in freezing (or nearly freezing) temperatures and the sensor for the light frames was reported to be in the region of 9° to 13°C.</span></li>
<li><span style="font-family: Arial, Helvetica, sans-serif;">My solution was to use a mini-fridge (a portable camping type fridge with a small thermoelectric cooler in the base). I evicted my stash of beer and placed the camera inside with cables to the laptop trailing out of the door, then sealed the whole thing up with black duct tape to keep as much light and warm air out as possible. After an hour or two the walls of the fridge were cooler than the reported probe temperatures inside the camera, thus (I hoped) reducing IR leakage through the camera cap as a potential source of problems.</span></li>
<li><span style="font-family: Arial, Helvetica, sans-serif;">When I started taking dark frames, I found that the probe temperature was still higher than that for the light frames, so for my second attempt I put freezer ice packs around the camera to supplement the fridge's rather puny cooler. This enabled me to take darks at similar temperatures to the lights, but I did have to take more care to avoid condensation dripping in to the camera's electronics.</span></li>
<li><span style="font-family: Arial, Helvetica, sans-serif;">Even so I found that after a few ten minute dark frames, the probe temperature would start to creep inexorably upwards. By adding a 20 to 30 minute pause between each dark exposure so the camera could cool I was able to get the probe temperature stay in the region of 9 - 13°C, thus matching the typical probe temperatures of my light frames. (Your own mileage will undoubtedly vary).</span></li>
<li><span style="font-family: Arial, Helvetica, sans-serif;">I used <a href="http://ideiki.com/astro/" target="_blank">APT</a> to run the camera on a programmed sequence of dark frame exposures and pauses, so I could happily set up in the morning and come back at the end of the day having bagged perhaps 15 or so useful darks. It took me several weekends to build up sufficient numbers of exposures at each temperature to continue with the experiment.</span></li>
</ul>
<div>
<b style="font-family: Arial, Helvetica, sans-serif;"><span style="color: orange;">Is the Camera's Temperature Probe Reliable?</span></b><br />
<br />
<span style="font-family: Arial, Helvetica, sans-serif;">So with my entire library of darks in hand, I turned to the first problem. Is it possible to ensure that dark frames are taken at the same temperature as the light frames using an uncooled DSLR?</span><br />
<br />
<span style="font-family: Arial, Helvetica, sans-serif;">Canon cameras do have a temperature probe somewhere inside the camera body, and the temperature registered by the probe is recorded in the <a href="http://en.wikipedia.org/wiki/Exchangeable_image_file_format" target="_blank">EXIF</a> data in the RAW image file. Your camera software may contain a utility that allows you to inspect the EXIF data, but if not you could try something like <a href="http://www.sno.phy.queensu.ca/~phil/exiftool/" target="_blank">ExifTool</a>. Most usefully, when using an imaging package like <a href="http://www.ideiki.com/astro/" target="_blank">APT</a> or <a href="http://www.backyardeos.com/" target="_blank">BackyardEOS</a> it is also possible to have the probe temperature form part of the image's file name when it is created.</span><br />
<br />
<span style="font-family: Arial, Helvetica, sans-serif;"><b>So the first test was to determine whether the camera's temperature probe accurately reflects the temperature of the sensor over the duration of an exposure.</b> If so, it would be simple to sort and match dark and light frames by reference to their recorded probe temperatures.</span></div>
<div>
<span style="font-family: Arial, Helvetica, sans-serif;"></span><br />
<div>
<span style="font-family: Arial, Helvetica, sans-serif;">In theory, the median brightness of a dark frame should be proportional to both the sensor temperature and the exposure duration, and in practice this is usually the case for well-behaved CCD cameras. (See </span><span style="font-family: Arial, Helvetica, sans-serif;">"<a href="http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA479357" target="_blank">Evaluation of the accuracy of the dark</a> </span><span style="font-family: Arial, Helvetica, sans-serif;"><a href="http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA479357" target="_blank">frame subtraction method in CCD image </a></span><span style="font-family: Arial, Helvetica, sans-serif;"><a href="http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA479357" target="_blank">processing</a>" - Lévesque, Martin P. & </span><span style="font-family: Arial, Helvetica, sans-serif;">Lelièvre, </span><span style="font-family: Arial, Helvetica, sans-serif;">Mario</span><span style="font-family: Arial, Helvetica, sans-serif;">).</span></div>
<span style="font-family: Arial, Helvetica, sans-serif;"></span><br />
<div>
<span style="color: orange; font-family: Arial, Helvetica, sans-serif;"><b>Note: We use the <a href="http://en.wikipedia.org/wiki/Median" target="_blank">Median</a> brightness as this is less susceptible to outliers in the image like hot pixels or cosmic ray hits than the <a href="http://en.wikipedia.org/wiki/Mean" target="_blank">Mean (average)</a> brightness would be.</b></span></div>
<span style="font-family: Arial, Helvetica, sans-serif;"></span><br />
<span style="font-family: Arial, Helvetica, sans-serif;">If the temperature probe is reliable, two dark frames with the same median brightness should also have the same EXIF temperature assuming their exposure durations and ISO settings are also equal. </span><span style="font-family: Arial, Helvetica, sans-serif;">To test whether this was applicable to my Canon 500D I measured the median brightness of each of my entire library of 213 dark frames (all of which are ten minute exposures taken at ISO400).</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"></span><br />
<span style="font-family: Arial, Helvetica, sans-serif;">I needed a simple way to measure the statistics of a large set of images. Originally I used</span><span style="font-family: Arial, Helvetica, sans-serif;"> ImageJ, available from: </span><span style="font-family: Arial, Helvetica, sans-serif;"><a href="http://imagej.nih.gov/ij/index.html" target="_blank">http://imagej.nih.gov/ij/index.html</a></span><br />
<ul>
<li><span style="font-family: Arial, Helvetica, sans-serif;">Using the <em><span style="color: orange;">'Plugins -> Analyze -> Batch Measure'</span></em> option in ImageJ you can obtain a fair few different statistics from a set of images and save them to a text file for analysis.</span></li>
</ul>
<span style="font-family: Arial, Helvetica, sans-serif;">Unfortunately I later found that I wanted additional statistics that are not available in ImageJ but are available in PixInsight's <i><span style="color: orange;">Statistics</span></i> process. The latter tool can only be used on a single image at a time, and all the cutting and pasting of numbers soon became rather tiresome. The 'simple' answer was to take a year out of this project and write the PixInsight <i><span style="color: orange;">BatchStatistics</span></i> script (<a href="http://pixinsight.com/forum/index.php?topic=7875.0" target="_blank">details here</a>). </span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"></span><br />
<div>
<span style="font-family: Arial, Helvetica, sans-serif;">Fortunately my script is now part of the official PixInsight distribution, so you can skip ahead a year in your own experiments! </span><span style="font-family: Arial, Helvetica, sans-serif;">I ran the <i><span style="color: orange;">BatchStatistics</span></i> script with the following settings:</span></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgzHwRA3WQEBK4lwZimijSnlT3aLvsGAw5qsOGoaGezNSexCkjDbNBRrsPmBT3ODo1kYw_WTNyjK0sxmrl73NXpg2b0aKEe7623WWxMXZR1ynelQJC2-QB102h3JXNBzf6Kc-BW4AITLes/s1600/BatchStatistics.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgzHwRA3WQEBK4lwZimijSnlT3aLvsGAw5qsOGoaGezNSexCkjDbNBRrsPmBT3ODo1kYw_WTNyjK0sxmrl73NXpg2b0aKEe7623WWxMXZR1ynelQJC2-QB102h3JXNBzf6Kc-BW4AITLes/s1600/BatchStatistics.png" height="640" width="520" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="color: orange; font-family: Arial, Helvetica, sans-serif; font-size: small;">BatchStatistics Script Settings</span></td></tr>
</tbody></table>
</div>
<div>
<ul>
<li><span style="font-family: Arial, Helvetica, sans-serif;">Use the <em><span style="color: orange;">'Add Files..'</span></em> button to add all the dark frames that you want to measure to the file list.</span></li>
<li><span style="font-family: Arial, Helvetica, sans-serif;">Uncheck the <em><span style="color: orange;">'Normalize'</span></em> and <em><span style="color: orange;">'Unclipped'</span></em> check boxes, and set the <em><span style="color: orange;">'Number Format'</span></em> to something appropriate. </span><span style="font-family: Arial, Helvetica, sans-serif;">By default PixInsight converts the integer ADU values to its Normalized Real format. If you want the values in camera ADUs instead, then you'd select the appropriate bit depth from the <em><span style="color: orange;">'Number Format'</span></em> drop-down. Canon DSLRs normally use 12 bit or 14 bit format depending on the model, and most modern CCD cameras use 16 bit format.</span></li>
<li><span style="font-family: Arial, Helvetica, sans-serif;">Check <em><span style="color: orange;">'Full File Name'</span></em>, <em><span style="color: orange;">'Median'</span></em> and <em><span style="color: orange;">'Median Absolute Deviation (MAD)'</span></em> as the statistics to output.</span></li>
<li><span style="font-family: Arial, Helvetica, sans-serif;">Use the <em><span style="color: orange;">'Output File..'</span></em> button to set a file name and location for the statistics, and choose <em><span style="color: orange;">'CSV'</span></em> as the <em><span style="color: orange;">'File Format'</span></em>.</span></li>
<li><span style="font-family: Arial, Helvetica, sans-serif;">Use the <em><span style="color: orange;">'Analyse'</span></em> button to generate the statistics. Note that the more statistics options you choose, the longer this process will take, so only use the ones you really need.</span></li>
<li><span style="font-family: Arial, Helvetica, sans-serif;">You can then open the resulting output file in Microsoft Excel (though any spread sheet will do, e.g. OpenOffice, Google Drive, etc.) Excel has a wizard which will guide you through importing the CSV formatted data. A sample of the results after importing is shown below:</span></li>
</ul>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEggQyo5g0JwMgx7yMKtOsh3mE2x-0Y3IR1OLi12JNiUVwXNPBodkVfd3gK61wddHB5rSfccabdj_qDzhT5OBsNt86cIP3vFzR65QevXpDoxqd77BCZ0wJ_o5ODECYXGiIq830JU-v8Shho/s1600/Stats_Sample.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEggQyo5g0JwMgx7yMKtOsh3mE2x-0Y3IR1OLi12JNiUVwXNPBodkVfd3gK61wddHB5rSfccabdj_qDzhT5OBsNt86cIP3vFzR65QevXpDoxqd77BCZ0wJ_o5ODECYXGiIq830JU-v8Shho/s1600/Stats_Sample.png" height="105" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="color: orange; font-family: Arial, Helvetica, sans-serif; font-size: small;">Statistics Imported in to Excel</span></td></tr>
</tbody></table>
<ul>
<li><span style="font-family: Arial, Helvetica, sans-serif;">Note that the columns headed <em><span style="color: orange;">'Median_0'</span></em> and <em><span style="color: orange;">'MAD_0'</span></em> are the median and median absolute deviation of the first channel in each image. These greyscale dark frames only have a single channel (channel 0).</span></li>
<li><span style="font-family: Arial, Helvetica, sans-serif;">Next I manually added a column <em><span style="color: orange;">'Temp'</span></em> and entered the EXIF temperature of each dark frame, which I obtained from the file name,</span></li>
<li><span style="font-family: Arial, Helvetica, sans-serif;">I also created a <span style="color: orange;">'Date-Time'</span> column and entered the date and time of capture of each dark frame, again from the file name.</span></li>
<li><span style="font-family: Arial, Helvetica, sans-serif;">Finally I sorted the entire list in ascending order of capture date and time (using Excel's <span style="color: orange;">'Sort'</span> function).</span></li>
</ul>
<span style="font-family: Arial, Helvetica, sans-serif;">A small section of the final set of data in 14 bit ADU format is shown below:</span><br />
<div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj_WSVV8tC5S_4DPx73kwR9OZCdl4aYFe3e5LyhW14EVKxnMFBWdCTsU-GsrTMaovW8OnjUv6bKYMjJfEgiG4NlEXnVlHth344hRwsrRc0t5niYy9YfTmsQVi6vn92rWVQf8Xoywwcbrws/s1600/dark+data.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj_WSVV8tC5S_4DPx73kwR9OZCdl4aYFe3e5LyhW14EVKxnMFBWdCTsU-GsrTMaovW8OnjUv6bKYMjJfEgiG4NlEXnVlHth344hRwsrRc0t5niYy9YfTmsQVi6vn92rWVQf8Xoywwcbrws/s1600/dark+data.png" height="218" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="color: orange; font-family: Arial, Helvetica, sans-serif; font-size: small;">Dark Frame Data Sorted by Temperature</span></td></tr>
</tbody></table>
</div>
<span style="color: orange; font-family: Arial, Helvetica, sans-serif;"><strong>Checking for Outliers</strong></span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"></span><br />
<span style="font-family: Arial, Helvetica, sans-serif;">Next I plotted the average brightness (Median) of each image against the temperature reported by the camera sensor (Temp) on a line graph to obtain the following:</span><br />
<div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjyotAjPNHBUFEeM6ORFSr2YzRQqrXafwgCt4dz_VsCrQResQaLIQNNrLXm_8q0WyJz2pmgHRcYA8pBa-VAwwrxdI81_5IUQE0LvzLBjrPOnjhdfulSpxqtkpYMul3y60uVpmpqnwGJkeU/s1600/median_temp_all.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjyotAjPNHBUFEeM6ORFSr2YzRQqrXafwgCt4dz_VsCrQResQaLIQNNrLXm_8q0WyJz2pmgHRcYA8pBa-VAwwrxdI81_5IUQE0LvzLBjrPOnjhdfulSpxqtkpYMul3y60uVpmpqnwGJkeU/s1600/median_temp_all.png" height="396" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="color: orange; font-family: Arial, Helvetica, sans-serif; font-size: small;">Median and Temperature of Dark Frames</span></td></tr>
</tbody></table>
</div>
<span style="font-family: Arial, Helvetica, sans-serif;">So what does this tell us?
</span><br />
<ul>
<li><span style="font-family: Arial, Helvetica, sans-serif;">The EXIF temperature (orange line) fluctuates quite markedly over time. Bear in mind that these dark frames were captured in multiple sessions and not in a continuous sequence, so we'd expect some big temperature jumps between the end of a session and the start of the next one. Nonetheless, on examining the data, it was quite clear that the reported temperature fluctuated a lot over the course of individual sessions despite my best efforts to control it.</span></li>
<span style="font-family: Arial, Helvetica, sans-serif;">
</span>
<li><span style="font-family: Arial, Helvetica, sans-serif;">The median brightness (blue line) stayed relatively stable, except for a small spike in one of the early sessions at the left of the graph and a really big spike in another session at the middle of the graph.</span></li>
</ul>
<div>
<span style="font-family: Arial, Helvetica, sans-serif;">These two spikes in the medians clearly warranted attention, so I looked more closely at the dates and times of the relevant frames.
</span></div>
<ul>
<li><span style="font-family: Arial, Helvetica, sans-serif;">It was clear that frames in the big spike were taken from shortly before sunrise until a few hours after it. I wracked my brain and recalled that I had left my scope and camera set up taking darks at the end of an imaging session, but had clearly not made it out of bed early enough to stop daylight leaking in to the camera.</span></li>
<span style="font-family: Arial, Helvetica, sans-serif;">
</span>
<li><span style="font-family: Arial, Helvetica, sans-serif;">Similarly the frames in the small spike were a few taken during the middle of the day at a time before I started my camera-cooling experiments in the light-proof fridge.</span></li>
</ul>
<div>
<span style="font-family: Arial, Helvetica, sans-serif;">Notice that the EXIF temperature increased significantly for these 'outlier' dark frames. This is not surprising as I was not making any effort to keep the camera cool. What <u>is</u> important are the equally large spikes in the temperature at other times during dark frame capture.</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"></span><br />
<strong><span style="font-family: Arial, Helvetica, sans-serif;">The first lesson we have learned is to be wary of relying on the camera's temperature sensor alone to judge the quality of dark frames. By measuring the images statistically, it was relatively easy for me to identify and weed out any rogue frames cause by poor technique or other transient issues.</span></strong></div>
<br />
<div>
<span style="color: orange; font-family: Arial, Helvetica, sans-serif;"><strong>Analysing the Dark Frames</strong></span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"></span><br />
<span style="font-family: Arial, Helvetica, sans-serif;">Next I pruned my set of results to remove those outlier frames that had clearly suffered from external light leaking in to the camera. </span><span style="font-family: Arial, Helvetica, sans-serif;">Plotting the only the good 'inlier' frames, I got the following:</span></div>
<div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh0Lq9SZGauaAE2LpeHCb7QMI1yKQmw5ElqhSmg6_KYV9SfUpq1E6vSZDuz_AuTJqpOLW3g8Io2F1cIB41bL6gbz8gNLFkUXp5Ua8RvqaDaU3vRV1g-w0aFLcQD7XeG6hXH1voHhyLm9i4/s1600/median_temp_inliers.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh0Lq9SZGauaAE2LpeHCb7QMI1yKQmw5ElqhSmg6_KYV9SfUpq1E6vSZDuz_AuTJqpOLW3g8Io2F1cIB41bL6gbz8gNLFkUXp5Ua8RvqaDaU3vRV1g-w0aFLcQD7XeG6hXH1voHhyLm9i4/s1600/median_temp_inliers.png" height="396" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="color: orange; font-family: Arial, Helvetica, sans-serif; font-size: small;">Median and Temperature of Inliers</span></td></tr>
</tbody></table>
</div>
<span style="font-family: Arial, Helvetica, sans-serif;">This graph shows that the median brightness (blue line / left axis) does fluctuate with temperature, but on a relatively small scale. Generally speaking, as the temperature increases the median brightness decreases.</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"></span><br />
<span style="font-family: Arial, Helvetica, sans-serif;">The graph below shows this relationship between temperature and median brightness much more clearly (note that the darker orange data points are where many frames have the same values):</span><br />
<div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj2lPhtbJE1OoP7Cg1D-PaOmxqkQPMMevrdn6-3Xo34M0DtWH2aIafvhHxCXo89J9RacwRTKcAcxjSEvpAsmXvx4hi9vbvxVjczKGgVTdLEk7oKt3a3guPQE4SsKRyT2ZVzmKxuzKJHIu8/s1600/temperature_v_median_inliers.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj2lPhtbJE1OoP7Cg1D-PaOmxqkQPMMevrdn6-3Xo34M0DtWH2aIafvhHxCXo89J9RacwRTKcAcxjSEvpAsmXvx4hi9vbvxVjczKGgVTdLEk7oKt3a3guPQE4SsKRyT2ZVzmKxuzKJHIu8/s1600/temperature_v_median_inliers.png" height="418" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="color: orange; font-family: Arial, Helvetica, sans-serif; font-size: small;">Temperature vs Median</span></td></tr>
</tbody></table>
</div>
<span style="font-family: Arial;"><strong>As you can see, the brightness of a dark frame reduces as the temperature increases. This is exactly the opposite of what we would expect if we assume that the EXIF temperature corresponds to the true temperature of the sensor.</strong></span><br />
<span style="font-family: Arial;"></span><br />
<span style="font-family: Arial;">In order to test this further, I next plotted the <a href="http://en.wikipedia.org/wiki/Median_absolute_deviation" target="_blank">Median Absolute Deviation (MAD)</a> of each frame against the EXIF temperature:</span><br />
<div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiAS_wouvv4iGlyW8am2UTdgH82PLr_8XcY-EMBoylxBHxj9nmWrUOpPTtXihKo0pvk8er5ClJ5IVfivgHkMNODl2UwbqZznddWu91O83NLaiAMqMPYAt5e6hrglSe6m-Pl5MQoP-mp9p8/s1600/mad_temp_inliers.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiAS_wouvv4iGlyW8am2UTdgH82PLr_8XcY-EMBoylxBHxj9nmWrUOpPTtXihKo0pvk8er5ClJ5IVfivgHkMNODl2UwbqZznddWu91O83NLaiAMqMPYAt5e6hrglSe6m-Pl5MQoP-mp9p8/s1600/mad_temp_inliers.png" height="396" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="color: orange; font-family: Arial, Helvetica, sans-serif; font-size: small;">MAD and Temperature of Inliers</span></td></tr>
</tbody></table>
</div>
<span style="font-family: Arial;">The MAD is a measure of variability of the individual pixel values in an image. Given that my dark frames are a set of (nearly) identical images, any change in the MAD between images should be proportional to the amount of noise that each contains. Given that dark current and dark current noise both increase as temperature increases, the MAD enables us to</span><span style="font-family: Arial;"> double-check the strange result above. <strong>You can see from the graph above that the MAD (generally) increases with temperature as we'd expect.</strong></span><br />
<strong><span style="font-family: Arial;"></span></strong><br />
<span style="color: orange; font-family: Arial, Helvetica, sans-serif;"><strong>Note: We use the MAD in preference to the <a href="http://en.wikipedia.org/wiki/Standard_deviation" target="_blank">Standard Deviation</a> or <a href="http://en.wikipedia.org/wiki/Variance" target="_blank">Variance</a> as it is a more robust estimator of scale, i.e. outliers like hot pixels and cosmic ray hits won't affect our results as much.</strong></span><br />
<br />
<span style="font-family: Arial;">Again, the graph below shows this relationship more clearly:</span>
<br />
<div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhHl85OHbsmUssFOL9DKCwgwDWVfOw9pEcN0Ntc2oHceZhEA7bf6PnsZOfS5Na8ezDFInbE1UcxzwWRqig7a3N7tXUJjoywGKGaIumrkrTSlmmDlqQdSKLysC-HXuzE3Xljml5ao27-ldc/s1600/temperature_v_mad_inliers.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhHl85OHbsmUssFOL9DKCwgwDWVfOw9pEcN0Ntc2oHceZhEA7bf6PnsZOfS5Na8ezDFInbE1UcxzwWRqig7a3N7tXUJjoywGKGaIumrkrTSlmmDlqQdSKLysC-HXuzE3Xljml5ao27-ldc/s1600/temperature_v_mad_inliers.png" height="414" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="color: orange; font-family: Arial, Helvetica, sans-serif; font-size: small;">Temperature vs MAD</span></td></tr>
</tbody></table>
</div>
<span style="font-family: Arial, Helvetica, sans-serif;"><strong>So we now have contradictory findings; the MAD increases with temperature, but the median unexpectedly decreases. Why should that be?</strong></span><br />
<strong><span style="font-family: Arial;"></span></strong><br />
<span style="font-family: Arial;"><strong><span style="color: orange;">On-Camera Processing</span></strong></span><br />
<br />
<span style="font-family: Arial;">To be perfectly honest, I wasn't that surprised. As noted by Craig Stark in his article <a href="http://www.stark-labs.com/craig/resources/Articles-&-Reviews/CanonLinearity.pdf" target="_blank">Profiling the Long-Exposure Performance of a Canon DSLR</a>, the RAW image files produced by Canon DSLRs are not the same as the 'pure' output files created by an astronomical CCD camera. The Canon pre-processes the image on-camera before creating the RAW file, whereas a CCD will typically give you an unadulterated measurement direct from each sensor element.</span></div>
<div>
<span style="font-family: Arial;">
<span style="font-family: Arial, Helvetica, sans-serif;"></span></span> </div>
<div>
<span style="font-family: Arial;"><span style="font-family: Arial, Helvetica, sans-serif;">You can read the details in Craig's article, but in short, the Canon DSLR seems to try to minimise the appearance of dark current. In his tests, Craig found that dark frames get darker as the exposure length increases, at least for shorter exposures. He also found that the trend reversed for longer exposures with the dark frames brightening again.</span></span></div>
<div>
<span style="font-family: Arial;">
</span> </div>
<div>
<span style="font-family: Arial;">
<span style="font-family: Arial, Helvetica, sans-serif;">My own tests reproduce the first part of this result, showing that the <u>appearance</u> of dark current decreases as sensor temperature increases. In both types of test, measuring the dark current noise shows that more dark current has accumulated (as required by the laws of physics!), but that the camera processes the image to make it appear darker instead of brighter.</span></span></div>
<div>
<span style="font-family: Arial;">
</span> </div>
<div>
<span style="font-family: Arial;">
</span><span style="font-family: Arial, Helvetica, sans-serif;"><strong>On a more positive note, it is clear that for my Canon 500D, the temperature sensor does bear some relationship to the imaging sensor, as demonstrated by the "EXIF Temperature vs MAD" graph above. Subject to the caveat about eliminating outliers noted above, in the case of this particular camera it would be reasonable to use the reported temperature to match dark frames together in order to create a master dark.</strong></span></div>
<span style="font-family: Arial, Helvetica, sans-serif;"></span><br />
<span style="font-family: Arial, Helvetica, sans-serif;">That said, there are several reasons why the temperature sensor in other camera models may not always be an accurate guide to the mean temperature of the sensor during the whole exposure:</span>
<br />
<div>
<ul>
<li><span style="font-family: Arial, Helvetica, sans-serif;">The probe may not be located sufficiently close the sensor to give a useful reading.</span></li>
<li><span style="font-family: Arial, Helvetica, sans-serif;">The probe may not heat up and cool down at the same rate as the sensor, e.g. it may be attached to something that has a large thermal mass that initially slows the temperature rise of the probe and subsequently reduces the rate at which it cools vs the rate of heating/cooling of the sensor itself. Alternatively it may be near another component that generates its own heat (processing chips, the battery, etc.)</span></li>
<li><span style="font-family: Arial, Helvetica, sans-serif;">There have been some reports that the main purpose of the temperature sensor in Canon DSLRS is to monitor the chips used to process live view and movie modes (in order to shut the camera down should they overheat due the intensive processing needed).</span></li>
<li><span style="font-family: Arial, Helvetica, sans-serif;">For Canon cameras, the probe temperature is recorded at the </span><u style="font-family: Arial, Helvetica, sans-serif;">start</u><span style="font-family: Arial, Helvetica, sans-serif;"> of each exposure. Since the camera is not cooled, the sensor may heat up during a long exposure. Thus the temperature measured at the start doesn't necessarily reflect the temperature at the end of the exposure. (Though we might look at the temperature at the start of the <u>next</u> exposure to get a rough idea of the temperature at the end of the previous one provided we don't wait too long between exposures.)</span></li>
<li><span style="font-family: Arial, Helvetica, sans-serif;">We don't know if the sensor heats up linearly during the exposure. If it does then we could average the start and (rough) end temperatures of each exposure to match darks and lights which have the same averages. If the sensor heats non-linearly or unpredictably, then we may be wasting our time. Bear in mind that it is usually the case that much more heat is generated when the image is being read out of the sensor at the end of an exposure, suggesting a non-linear heating/cooling cycle.</span></li>
<li><span style="font-family: Arial, Helvetica, sans-serif;">The overriding problem is that we have no practical way to measure any of this, short of disassembling the camera and installing our own temperature probe attached to the imaging sensor.</span></li>
</ul>
</div>
<span style="font-family: Arial, Helvetica, sans-serif;">If you perform the same sort of tests that I have and you discover a clear correlation between the MAD of your dark frames and the EXIF temperature, then you can use the temperature to match dark frames together in order to create a good master dark.</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"></span><br />
<span style="color: orange; font-family: Arial, Helvetica, sans-serif;"><strong>Alternatives to Temperature</strong></span><br />
<span style="font-family: Arial;"></span><br />
<span style="font-family: Arial, Helvetica, sans-serif;">If you don't find such a correlation, then try plotting the medians against the MADs as in the graph below:</span><br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhqzN1u6-fx9SqrcDTeBLcK56MAF29kRGl4VwB4jFSh0fR5Usz256GXMYEXxcl3qvtYEaroIEDrElFRTLzW-VBgdjg70eEQKszmHzdlxDqm1lohodF4gXhqYX_Nvd2sl0kyLBkDzKk-VU0/s1600/median_v_mad_inliers.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhqzN1u6-fx9SqrcDTeBLcK56MAF29kRGl4VwB4jFSh0fR5Usz256GXMYEXxcl3qvtYEaroIEDrElFRTLzW-VBgdjg70eEQKszmHzdlxDqm1lohodF4gXhqYX_Nvd2sl0kyLBkDzKk-VU0/s1600/median_v_mad_inliers.png" height="400" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="color: orange; font-family: Arial, Helvetica, sans-serif; font-size: small;">Median Brightness vs MAD</span></td></tr>
</tbody></table>
<span style="font-family: Arial;"></span><span style="font-family: Arial;">Unsurprisingly, you can see that there is a clear correlation between the median brightness and the MAD (albeit the line goes down instead of up due to the Canon's on-camera processing).</span><br />
<ul>
<li><span style="font-family: Arial;">If your own graph shows a similar correlation, then you can try to match dark frames using the MAD instead of the EXIF temperature, as I'll show in the next part of this series.</span></li>
<li><span style="font-family: Arial;">If there is no clear correlation between these two values then you're out of luck. It might be that your DSLR is also performing some kind of noise reduction on the image before you get hold of it. All you can do is take your best guess at matching dark frames to make a master and test their effect on your images. Again I'll show you how to do this later in the series.</span></li>
</ul>
<span style="font-family: Arial, Helvetica, sans-serif;"><b>The key conclusion is that you need to use some simple statistics to check the dark frames produced by your camera. Be wary of relying on recipes provided by others and perform your own tests for your own camera.</b></span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"></span><br />
<span style="font-family: Arial;">In the next part of this series, we'll look at creating and testing master darks, as well as methods for matching DSLR dark frames to light frames for best results.</span>Unknownnoreply@blogger.com5tag:blogger.com,1999:blog-4541271552202931674.post-30349123627634714992015-02-09T14:43:00.003+00:002015-06-15T14:04:35.290+01:00PixInsight DSLR Workflow - Part 1b, Superbias<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjrfukI0RNJCdayn6oPlcDKTdJLFGRjMjbSoaOJLfXtTCAYurmVuuPoyMsN1s27lEKQkmX8iGftjZJcWX0IWF2xCWf39efZRk0oNWN1NEf2t5aBe4dRYg7d_U2SoGk2vw7gStgnbapRsE8/s1600/Superbias_Result_10.png" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"><img border="0" height="133" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjrfukI0RNJCdayn6oPlcDKTdJLFGRjMjbSoaOJLfXtTCAYurmVuuPoyMsN1s27lEKQkmX8iGftjZJcWX0IWF2xCWf39efZRk0oNWN1NEf2t5aBe4dRYg7d_U2SoGk2vw7gStgnbapRsE8/s1600/Superbias_Result_10.png" width="200" /></a><span style="font-family: Arial, Helvetica, sans-serif;">This is the second in a series of posts explaining the general workflow I follow when using PixInsight. We're going to take a quick look at improving our bias frames still further, using PixInsight's <i><span style="color: orange;">SuperBias</span></i> module.</span><br />
<br />
<span style="font-family: Arial, Helvetica, sans-serif;">Read on for more on about creating a good super bias. </span><span style="font-family: Arial, Helvetica, sans-serif;">(If you've arrived part way through, start the series here with </span><a href="http://www.blackwaterskies.co.uk/2013/09/pixinsight-dslr-workflow-part-1-bias.html" style="font-family: Arial, Helvetica, sans-serif;">Bias Frames</a><span style="font-family: Arial, Helvetica, sans-serif;">).</span><br />
<br />
<a name='more'></a><span style="color: orange; font-family: Arial, Helvetica, sans-serif;"><b>Improving Bias Frames</b></span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span><span style="font-family: Arial, Helvetica, sans-serif;">As we saw in <a href="http://www.blackwaterskies.co.uk/2013/09/pixinsight-dslr-workflow-part-1-bias.html" target="_blank">Part 1</a>, we can measure (and eventually subtract) the fixed pattern created by a DSLR by integrating a large stack of bias frames (very short exposures with no light hitting the sensor). The more individual bias frames we add to the stack, the better the Signal to Noise Ratio (SNR) of the resulting master bias frame.</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;">Whilst it doesn't take long to capture a few hundred bias frames, there is a practical limit to how many PixInsight can stack, depending on the amount of memory your computer has. Additionally, the more frames you use, the longer and longer the <i><span style="color: orange;">ImageIntegration</span></i> process will take to complete. Given the marginal improvements of adding new frames, I suggested that there was no point in continuing beyond about 160-180 bias frames. But what if there was a method to get the benefit of stacking thousands of frames without the time and effort?</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="color: orange; font-family: Arial, Helvetica, sans-serif;"><b>Superbias to the Rescue</b></span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;">PixInsight has a <i><span style="color: orange;">SuperBias</span></i> module that allows us to do exactly that, with one proviso: It will only work for a master bias frame that has a dominant pattern of vertical and/or horizontal stripes. If your camera produces a master bias with some other pattern, such as diagonal bands, stripes or something else, <i><span style="color: orange;">SuperBias</span></i> probably won't be of benefit.</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;">As you can see, my Canon 500D's master bias of 330 frames shows a dominant pattern of thin vertical stripes, with a secondary pattern of fainter large-scale horizontal bands:</span><br />
<div class="separator" style="clear: both; text-align: center;">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhgD4e8dlCYYXGko7CDFl7NTnt71MptmzzYl2ioom8FAZjV6jL9fNQnQv7CUZ-U6JSmLjfui3d1o3Ro5RGWkO2BSp0iwBBjOXoGVFCti7QLWDaAakvZ0QrU645Hy5ikTB5Aa-FfOzmbtBQ/s1600/Master_Bias.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="426" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhgD4e8dlCYYXGko7CDFl7NTnt71MptmzzYl2ioom8FAZjV6jL9fNQnQv7CUZ-U6JSmLjfui3d1o3Ro5RGWkO2BSp0iwBBjOXoGVFCti7QLWDaAakvZ0QrU645Hy5ikTB5Aa-FfOzmbtBQ/s1600/Master_Bias.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="color: orange; font-family: Arial, Helvetica, sans-serif; font-size: small;">Canon 500D Master Bias - 330 Frames</span></td></tr>
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<span style="font-family: Arial, Helvetica, sans-serif;">Notice that I've applied the PixInsight <b>Screen Transfer Function (STF)</b> to the master bias so that we can see what is going on; by default a bias frame would look black on screen due to the very low ADU values it contains.</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;">With my master bias, I found that applying the default settings of the <i><span style="color: orange;">SuperBias</span></i> module to it gave the best results, as shown below:</span><br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjFJy_7t61_p098CPO_cMI996Y1a5NpsPHTNzcVHZeYbLp1e_6m7Pg9xMWhYP5tGXiH529yPALtW8cbR-GE7Y_ee0AGc-3kk4jd9RX2niAYxGjdRPi-UiEcBhwi53BE8XfbOZL0urxmVXQ/s1600/Superbias.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="153" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjFJy_7t61_p098CPO_cMI996Y1a5NpsPHTNzcVHZeYbLp1e_6m7Pg9xMWhYP5tGXiH529yPALtW8cbR-GE7Y_ee0AGc-3kk4jd9RX2niAYxGjdRPi-UiEcBhwi53BE8XfbOZL0urxmVXQ/s1600/Superbias.png" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="color: orange; font-family: Arial, Helvetica, sans-serif; font-size: small;">Superbias Module - Default Settings</span></td></tr>
</tbody></table>
<span style="font-family: Arial, Helvetica, sans-serif;">- Simply apply the module to your best master bias frame and evaluate the results visually after applying the same STF to both the master bias and the super bias.</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;">In my case, this is what I got from the default process settings:</span><br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjtS_g7QGLUbRCJEexzNWTy6JHpD-ld1LJfHBx8KSkRZPxet7IwGWUsoKBP4zZea5KlsdUGNREXghd4zTewEG7sUQQL4ywnRkwKRU_W3mwpklG1tK3GB9bpZ-hx-Xu0W0xSe3uW7OCOeZ8/s1600/Superbias_Result.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="427" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjtS_g7QGLUbRCJEexzNWTy6JHpD-ld1LJfHBx8KSkRZPxet7IwGWUsoKBP4zZea5KlsdUGNREXghd4zTewEG7sUQQL4ywnRkwKRU_W3mwpklG1tK3GB9bpZ-hx-Xu0W0xSe3uW7OCOeZ8/s1600/Superbias_Result.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="color: orange; font-family: Arial, Helvetica, sans-serif; font-size: small;">Mater Bias After Applying Default Superbias Settings</span></td></tr>
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<span style="font-family: Arial, Helvetica, sans-serif;">You can see that we now have a much clearer pattern of vertical stripes, and that the large scale horizontal bands also feature. The super bias has absolutely no random noise. <i><span style="color: orange;">Superbias</span></i> simulates the result of stacking thousands of individual bias frames.</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<b style="color: orange; font-family: Arial, Helvetica, sans-serif;">Superbias Settings</b><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;">There aren't many settings to play with in this module. The 'Orientation' setting should be changed if your master bias has a dominant horizontal or checkerboard pattern of stripes instead of a vertical one.</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;">The 'Multiscale layers' setting can be increased or decreased to preserve the large scale patterns in the master bias. As you can see below, increasing the number of layers to 10 reduces the effect of the large scale horizontal band pattern, especially along the top edge of the image, so I left it at the default 7 layers:</span><br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjfaQW9QfUauL6cEIoCjcTKgF1c05-4b2yPcfj2NqccT7Nr7syfbAbddCqkCxBwkAL-Y3yD_ZuzVmDXvUn36Cip0yhV7CmX6PgQP-wGWCpG41UZbcJmcErJ6MEc_8f9IM341V1cUnBrJV8/s1600/Superbias_Result_10.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="426" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjfaQW9QfUauL6cEIoCjcTKgF1c05-4b2yPcfj2NqccT7Nr7syfbAbddCqkCxBwkAL-Y3yD_ZuzVmDXvUn36Cip0yhV7CmX6PgQP-wGWCpG41UZbcJmcErJ6MEc_8f9IM341V1cUnBrJV8/s1600/Superbias_Result_10.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="color: orange; font-family: Arial, Helvetica, sans-serif; font-size: small;">Master Bias After Applying Superbias With 10 Layers</span></td></tr>
</tbody></table>
<span style="font-family: Arial, Helvetica, sans-serif;">I suggest you experiment with different values for the layers and/or orientation settings whilst comparing the results visually to see which gives the best match for the original master bias.</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<b style="color: orange; font-family: Arial, Helvetica, sans-serif;">The Final Test</b><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;">The final test of your super bias master is to subtract it from the original master bias frame, whilst remembering to add a </span><b style="font-family: Arial, Helvetica, sans-serif;">Pedestal.</b><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;"><br /></span></b></span>
<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;">Note: A pedestal is a small extra ADU value that you add to every pixel before subtracting one image from another. Due to the random nature of noise in images, subtraction operations can easily result in pixels with negative values. Since negative values aren't (usually) allowed in images, PixInsight will 'clip' them to zero. Thus careless application of bias and dark frames during image calibration can create unsightly black 'holes' all over your image.</span></b></span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;">To perform the subtraction, we use the <i><span style="color: orange;">PixelMath</span></i> process with the settings as shown below:</span><br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiD55oC3YfYVULJJYrfCJb-aA5sndYExw_Y5z7x7XvOnLABr6Kpg7sZGG43eFXNrQTLD3OlkvmaMaqiPBD8NxGGN3QCZRkCfTmyY-RJISvUQR-Yv4EiA6RSpXEXCOSHypjouXZTvhtuJ7c/s1600/Bias_Test.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="507" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiD55oC3YfYVULJJYrfCJb-aA5sndYExw_Y5z7x7XvOnLABr6Kpg7sZGG43eFXNrQTLD3OlkvmaMaqiPBD8NxGGN3QCZRkCfTmyY-RJISvUQR-Yv4EiA6RSpXEXCOSHypjouXZTvhtuJ7c/s1600/Bias_Test.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="color: orange; font-family: Arial, Helvetica, sans-serif; font-size: small;">PixelMath Expression for Testing SuperBias</span></td></tr>
</tbody></table>
<span style="font-family: Arial, Helvetica, sans-serif;">- In the "RGB/K" box, enter the following expression:</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<br />
<div style="text-align: center;">
<span style="font-family: Courier New, Courier, monospace;">(MASTER_BIAS + 0.01) - SUPER_BIAS</span></div>
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;">- Substitute the actual image name of the master bias where it says "MASTER_BIAS", and the super bias where it says "SUPER_BIAS". So in my case I have put the following:</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<br />
<div style="text-align: center;">
<span style="font-family: Courier New, Courier, monospace;">(MASTER_BIAS_1_4000s_400iso330Frames + 0.01)- MASTER_BIAS_1_4000s_400iso330Frames_Superbias_7</span></div>
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;">- You can use the "Expression Editor" button to get more help constructing expressions. For example, the names of all open images are available to double click and insert in to the expression.</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;">- Under the "Destination" section I have selected "Create new image"; the default is to overwrite the target image but I want to keep my original master bias for comparison purposes. Leave all the other settings at the defaults.</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;">- Finally click the blue square "Apply" button to execute the expression and a new image window should appear with the result of the subtraction.</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;">This pixel math expression takes each pixel value in the master bias image, adds a pedestal of 0.01 to the value of that pixel (to avoid creating any values less than zero as discussed), then subtracts the value of the corresponding pixel value from the super bias image and finally writes the result to the corresponding pixel in a new image.</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="color: orange; font-family: Arial, Helvetica, sans-serif;"><b>Note: We put the pixel math expression in the "RGB/K" input box because this is a single channel greyscale image ("K") which we haven't yet debayered it in to a colour image.</b></span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;">The resulting image looks like this:</span><br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgU49sUbU2tzrgF2n92pIfEJuoh2U305Z5dteBVjeRLnotjBkc_DXqEYMN6GR-Gow5Hnlio5X3PZ2fA_cHpnTrq2FqFq-81PoRkxrCX5HOdTwFu_OH6ywrTMQ34MO0Gut3KWSLFeYMyQUQ/s1600/Bias_Subtract_Test.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="428" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgU49sUbU2tzrgF2n92pIfEJuoh2U305Z5dteBVjeRLnotjBkc_DXqEYMN6GR-Gow5Hnlio5X3PZ2fA_cHpnTrq2FqFq-81PoRkxrCX5HOdTwFu_OH6ywrTMQ34MO0Gut3KWSLFeYMyQUQ/s1600/Bias_Subtract_Test.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="color: orange; font-family: Arial, Helvetica, sans-serif; font-size: small;">Result of Subtracting the Super Bias from the Master Bias</span></td></tr>
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<span style="font-family: Arial, Helvetica, sans-serif;">As you can see, it is composed of random noise with no visible patterns or other artefacts. This demonstrates that the super bias is a good one as it has successfully subtracted the fixed pattern from the master bias and left only the random noise behind. Thus the super bias will also be effective at removing the fixed pattern from dark, flat and light frames during calibration, but with the advantage of not adding its own contribution of noise to the calibrated images.</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;">If the result of the subtraction process had produced any visible stripes, bands or other artefacts, that would indicate that the <i><span style="color: orange;">Superbias</span></i> process was not effective; you should try different settings. If you can't find satisfactory</span><span style="font-family: Arial, Helvetica, sans-serif;"> </span><i style="font-family: Arial, Helvetica, sans-serif;"><span style="color: orange;">Superbias</span></i><span style="font-family: Arial, Helvetica, sans-serif;"> settings</span><span style="font-family: Arial, Helvetica, sans-serif;"> for your camera ,</span><span style="font-family: Arial, Helvetica, sans-serif;">leave it out of your workflow and use the standard master bias instead.</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="color: orange; font-family: Arial, Helvetica, sans-serif;"><b>Note: You can check whether the pedestal was sufficient using the PixInsight <i>Statistics</i> process. Examine the "minimum" pixel value in the result image. If it is greater than zero then the pedestal has done its job. If the "minimum" pixel value is zero, then it is likely that some clipping of negative values has occurred so try again with a larger pedestal value.</b></span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;">That's it for the <i><span style="color: orange;">Superbias</span></i> process. In the <a href="http://www.blackwaterskies.co.uk/2015/02/pixinsight-dslr-workflow-part-2a-dark.html">next instalment</a>, we'll be shedding some light on dark frames.</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>Unknownnoreply@blogger.com3tag:blogger.com,1999:blog-4541271552202931674.post-19093080936069045982014-11-05T19:44:00.002+00:002015-02-09T22:15:48.729+00:00M33 - The Triangulum Galaxy<span style="font-family: Arial, Helvetica, sans-serif;">M33 is three million light years away and the third big member of the Local Group of galaxies, along with the Milky Way and Andromeda.</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;">This was taken at quarter moon, but luckily on the opposite side of the sky.I tried three different integrations in PixInsight - normal, Bayer Drizzle (1x with 1.0 drop size) and Drizzle 2x with 0.9 drop size. The Bayer drizzle did a better job on the colour with less bleeding of colour in/out of stars, but resolution and overall quality doesn't seem much better than standard integration. This version presented above uses the standard drizzle to produce a 2x larger image with much better resolution. There is a noticeable difference in the size of small stars, roundness of larger stars and many more tiny stars in the galaxy arms. Even when down-sampled for presentation (4x in this case) the image is much superior to the non-drizzled version.</span><br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiOILSYPur64jAsdZLk6x2UbsThNZEy2mceLQXABWkPjpSPI4u0U69GTUHSTUjBx3OFHbDufkhopmCF1fDR8dX60UHj9YAYneNajA3di_0YoINURIQaY8GJ8_gmB0WCXSqsDyXzMObRCBU/s1600/M33_V3_4x.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiOILSYPur64jAsdZLk6x2UbsThNZEy2mceLQXABWkPjpSPI4u0U69GTUHSTUjBx3OFHbDufkhopmCF1fDR8dX60UHj9YAYneNajA3di_0YoINURIQaY8GJ8_gmB0WCXSqsDyXzMObRCBU/s1600/M33_V3_4x.png" height="480" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="color: orange; font-family: Arial, Helvetica, sans-serif; font-size: small;">M33</span></td></tr>
</tbody></table>
<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;">Imager:</span></b> Sky-Watcher Evostar 80ED DS-Pro, </span><span style="font-family: Arial, Helvetica, sans-serif;">Sky-Watcher 0.85x Focal Reducer, </span><span style="font-family: Arial, Helvetica, sans-serif;">Canon EOS 500D (Unmodified), </span><span style="font-family: Arial, Helvetica, sans-serif;">Hutech IDAS LPS P2 2", </span><span style="font-family: Arial, Helvetica, sans-serif;">APT - Astro Photography Tool</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;">Guider:</span></b> Orion ST80,</span><span style="font-family: Arial, Helvetica, sans-serif;"> QHY 5, PHD Guiding</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;">Mount:</span></b> Sky-Watcher NEQ6, </span><span style="font-family: Arial, Helvetica, sans-serif;"> AstroTortilla, EQMod</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;">Processing:</span></b> PixInsight 1.8</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;">Dates:</span></b> March 1st, 2014</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;">LIghts:</span></b> 61 x 300seconds ISO400 (~5.1</span><span style="font-family: Arial, Helvetica, sans-serif;"> hours)</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;">Darks:</span></b> 109</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;">Flats:</span></b> 102</span><br />
<b style="font-family: Arial, Helvetica, sans-serif;"><span style="color: orange;">Bias:</span></b><span style="font-family: Arial, Helvetica, sans-serif;"> 330 (PixInsight SuperBias)</span>Unknownnoreply@blogger.com1tag:blogger.com,1999:blog-4541271552202931674.post-27612172150498174862014-10-16T13:11:00.000+01:002014-10-17T09:32:56.492+01:00Basics Part 1: Understanding Aperture, Focal Length and Focal Ratios<div style="text-align: right;">
</div>
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjKAvCxR2bsgHCm8DjDU43pa2g96y_2yH8HqdPxaBr1TNb9Up-8ZlsLR-u_YFz-C_B1NtAQCdwo-vUzMhAwnktNF0AN8RSjQWMAEBr59h6Ydj-UZ_ODJ5zQsGbg2_2u6GVqma4K3B1efVw/s1600/focal+length+small.png" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjKAvCxR2bsgHCm8DjDU43pa2g96y_2yH8HqdPxaBr1TNb9Up-8ZlsLR-u_YFz-C_B1NtAQCdwo-vUzMhAwnktNF0AN8RSjQWMAEBr59h6Ydj-UZ_ODJ5zQsGbg2_2u6GVqma4K3B1efVw/s1600/focal+length+small.png" height="236" width="400" /></a><span style="font-family: Arial, Helvetica, sans-serif;">Questions about the best choice of equipment for astro-imaging come up quite frequently. In this first of a series of posts, I will start by explaining the basics of aperture, focal length focal ratios. </span><br />
<br />
<span style="font-family: Arial, Helvetica, sans-serif;">These troublesome topics cause many beginning imagers to jump to mistaken conclusions. I</span><span style="font-family: Arial, Helvetica, sans-serif;">f you bear with me you'll find out how they (and other things) affect imaging and consequently you will be able to make better informed choices about your equipment. Read on for more...</span><br />
<a name='more'></a><br />
<h3>
<b style="font-family: Arial, Helvetica, sans-serif;">So what is a focal ratio?</b></h3>
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<span style="font-family: Arial, Helvetica, sans-serif;">"Focal ratio" (f-ratio) is a common term you will come across in the world of photography. It is a number that is used as shorthand for the "speed" of a camera lens and is expressed as "f/2", "f/4", etc. Lower numbers are "faster" than higher numbers, meaning that you can take a photograph using a shorter exposure length with an f/2 lens than you can with an f/4 lens. The simple rules used in photography don't carry straight over to astro-imaging though, as we'll find out.</span><br />
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<h3>
<span style="font-family: Arial, Helvetica, sans-serif;">
<b style="font-family: Arial, Helvetica, sans-serif;">Calculating f-ratios</b></span></h3>
<span style="font-family: Arial, Helvetica, sans-serif;">
<br />
<span style="font-family: Arial, Helvetica, sans-serif;">The f-ratio of a camera lens or a telescope can be calculated very simply as:</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;"><span style="color: orange;">f-ratio</span> = <span style="color: orange;">focal length</span> / <span style="color: orange;">aperture</span></span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span><span style="font-family: Arial, Helvetica, sans-serif;"><i>So for example, my old Meade SCT has a focal length of 2,000mm and it has an aperture of 203mm (i.e. the mirror has a diameter of 203mm). Therefore its f-ratio is 2,000 / 203 =<b> f/9.85</b>. It is fairly common to round higher f-ratios up or down, so this scope was advertised as having a f-ratio of <b>f/10</b>.</i></span><br />
<i><span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;">To give another example, my SkyWatcher 80ED has a focal length of 600mm and an aperture of 80mm and thus it is an <b>f/7.5</b>.</span></i><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;">If you are using a focal reducer or a Barlow lens in your set-up, you should include the resulting decrease or increase in effective focal length in the calculation as follows:</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;"><span style="color: orange;">f-ratio</span> = <span style="color: orange;">focal length</span> x <span style="color: orange;">change factor</span> / <span style="color: orange;">aperture</span></span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;"><i>So if I use my 0.85x focal reducer with my 80ED, the calculation becomes 600mm x 0.85 (510mm effective focal length) with an aperture of 80mm equals <b>f/6.375</b> so let's call it <b>f/6.4</b>.</i></span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;"><i>Using a 2x Barlow the effective focal length becomes 600mm x 2 which is 1,200mm making for <b>f/15</b>.</i></span>
</span><br />
<div>
<span style="font-family: Arial, Helvetica, sans-serif;"><span style="font-family: Arial, Helvetica, sans-serif;"><i><br /></i></span></span></div>
<span style="font-family: Arial, Helvetica, sans-serif;">
<span style="color: orange; font-family: Arial, Helvetica, sans-serif;"><b>Note: The f-ratio is a dimensionless number, i.e. it does not have any units. Provided you use the same units for both aperture and focal length you can calculate the f-ratio correctly. Don't mix up mm and inches in one calculation!</b></span><br />
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<h3>
<span style="font-family: Arial, Helvetica, sans-serif;">
<b style="font-family: Arial, Helvetica, sans-serif;">A better definition of f-ratio</b></span></h3>
<span style="font-family: Arial, Helvetica, sans-serif;">
<br />
<span style="font-family: Arial, Helvetica, sans-serif;">Unfortunately that shorthand of equating f-ratios to speed or exposure time has the potential to be very misleading when it comes to astro-imaging. So let's use a more precise definition: </span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><b><br /></b></span><span style="font-family: Arial, Helvetica, sans-serif;"><b>The f-ratio determines how much light a telescope (or lens) will concentrate in to a given area.</b></span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;">So if I point my two telescopes at uniform source of light such as an overcast sky, the one with the lower f-ratio will illuminate a given area of the camera sensor more than the one with the higher f-ratio.</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;">Now you may think I'm just nit-picking here. Surely if a lower f-ratio illuminates the sensor more, then any object you are trying to image will appear brighter to your camera and thus you will be able to take a shorter exposure? Yes and no; the image will appear brighter but that doesn't necessarily mean you can take a shorter exposure. Bear with me a whilst we explore f-ratios a bit further and we'll come back to that point later in the series...</span><br />
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</span><br />
<h3>
<span style="font-family: Arial, Helvetica, sans-serif;">
<b style="font-family: Arial, Helvetica, sans-serif;">F-ratios and illumination</b></span></h3>
<span style="font-family: Arial, Helvetica, sans-serif;">
<br />
<span style="font-family: Arial, Helvetica, sans-serif;">Firstly, let's explore how much light you get for each f-ratio. The graph below shows how much <u>less</u> light would fall on a given area (say a pixel in your camera sensor) as you increase the f-ratio. I've arbitrarily chosen f/2 as the staring point and called that 100%, and then shown what percentage of light would fall in the same area on the camera sensor as we increase the f-ratio.</span><span style="font-family: Arial, Helvetica, sans-serif;"> </span><br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEglYENx3UDt5taP19wiXthcwznjKqRuCri_ck4h2a2qQQtmSNla9H9jsB2hBFP8q9EBUsF6oigEexnSX_1S29FwQMqRDQ2Z6Kh6fqd9gOoVwFCiKjMVNDYSN1bmkSETupdYPGGOVnQPZ88/s1600/f-ratio1.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEglYENx3UDt5taP19wiXthcwznjKqRuCri_ck4h2a2qQQtmSNla9H9jsB2hBFP8q9EBUsF6oigEexnSX_1S29FwQMqRDQ2Z6Kh6fqd9gOoVwFCiKjMVNDYSN1bmkSETupdYPGGOVnQPZ88/s1600/f-ratio1.png" height="312" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="color: orange; font-family: Arial, Helvetica, sans-serif; font-size: small;">Relative illumination with increasing f-ratios</span></td></tr>
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<span style="font-family: Arial, Helvetica, sans-serif;">The simple rule is that every time you <u>double</u> the f-ratio, you get a <u>quarte</u>r of the light of the previous ratio.</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;"><i>So for f/4 we get 25% of the light of f/2 in the same area, and for f/8 we get 25% of the light of f/4 and thus 6.25% of the light of f/2 (a quarter of a quarter).</i></span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><i><br /></i></span>
<span style="font-family: Arial, Helvetica, sans-serif;"><i>Bear in mind that I arbitrarily started at f/2, but the relationship applies to any series of f-ratios. So f/10 would give you a quarter of the illumination of f/5, and f/6 would give you a quarter of the illumination of f/3.</i></span><br />
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</span><br />
<h3>
<span style="font-family: Arial, Helvetica, sans-serif;">
<b style="font-family: Arial, Helvetica, sans-serif;">F-ratios and aperture</b></span></h3>
<span style="font-family: Arial, Helvetica, sans-serif;">
<br />
<span style="font-family: Arial, Helvetica, sans-serif;">There are two ways in which we can vary the f-ratio of our telescope (or lens). One way is to change the f-ratio by changing the aperture and keeping the focal length the same. I've illustrated this below:</span><span style="font-family: Arial, Helvetica, sans-serif;"> </span><br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhLZwfZ6Axp4l4Qimba7_sGbUKQMzbtC15MGLmhFa0ZA3xsfb_wtcowI77x4TesGLXbm95FuvNxF85zneMv7wNdPZLbvZGHgeEa7ZY3TwibDNGR_x-mzyvNejpPTa445Wpl0qmvasIxMHY/s1600/f-ratio3.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhLZwfZ6Axp4l4Qimba7_sGbUKQMzbtC15MGLmhFa0ZA3xsfb_wtcowI77x4TesGLXbm95FuvNxF85zneMv7wNdPZLbvZGHgeEa7ZY3TwibDNGR_x-mzyvNejpPTa445Wpl0qmvasIxMHY/s1600/f-ratio3.png" height="302" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="color: orange; font-family: Arial, Helvetica, sans-serif; font-size: small;">Relative illumination with decreasing aperture</span></td></tr>
</tbody></table>
<span style="font-family: Arial, Helvetica, sans-serif;"><i>So let's say we have a telescope with a focal length of 800mm. If we have an aperture of 400mm, then it is an f/2 scope, but if we reduce the aperture to 200mm it becomes an f/4 scope, and if we further reduce the aperture to 100mm then it becomes an f/8.</i></span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;">In terms of illumination, the relationship is the same as we explored for f-ratios above - <u>halve the aperture</u> (whilst keeping the same focal length) and you will get a <u>quarter of of the illumination</u>. There is no magic involved here, i</span><span style="font-family: Arial, Helvetica, sans-serif;">t's a simple matter of geometry.</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;">By halving the aperture of the objective, its light-gathering area is reduced to a quarter of the original. One quarter of the light coming in to the front of the scope equals one quarter of the light coming out of the back equals one quarter of the illumination (assuming we keep the <u>same focal length</u>).</span><br />
<br />
<span style="font-family: Arial, Helvetica, sans-serif;"><i>For example, an aperture of 200mm has an area of 31,416mm<sup>2 </sup>(pi x radius<sup>2</sup>). An aperture of 100mm aperture covers 7,854mm<sup>2</sup>. 7,854 / 31,416 = 0.25 (i.e. one quarter of the area).</i></span></span><br />
<div>
<span style="font-family: Arial, Helvetica, sans-serif;"><i><br /></i></span></div>
<div>
<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;">Note: Telescopes have fixed apertures, so if you want a bigger aperture you have to buy a bigger scope. Camera lenses have a <a href="http://en.wikipedia.org/wiki/Diaphragm_(optics)" target="_blank">Diaphragm</a> which allow the aperture to be made smaller or larger as required. If you are a photographer looking for your first telescope, it is easy to fall in to the trap of assuming that a faster f-ratio always equals more light when in fact it might be due to focal length...</span></b></span><span style="font-family: Arial, Helvetica, sans-serif;"><i><b><span style="color: orange;"><br /></span></b></i>
<br />
</span><br />
<h3>
<span style="font-family: Arial, Helvetica, sans-serif;">
<b style="font-family: Arial, Helvetica, sans-serif;">F-ratios and focal length</b></span></h3>
<span style="font-family: Arial, Helvetica, sans-serif;">
<br />
<span style="font-family: Arial, Helvetica, sans-serif;">The second option for changing the f-ratio is to change the focal length whilst keeping the aperture constant. In terms of illumination, the following occurs:</span><span style="font-family: Arial, Helvetica, sans-serif;"> </span><br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhpGrW2YQbLqVl3kqmUPLngc86kF0tCVqnu0Wnlnykn3Q0Em3kAqdhy68yPqGcCPecjFc92pMPmLAMPA2P7AV9L9M1DrJTV3rMNEtHXOgXKa2NC-JLSGz3SUVcx29-WN9BSJthJyP27fU8/s1600/f-ratio2.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhpGrW2YQbLqVl3kqmUPLngc86kF0tCVqnu0Wnlnykn3Q0Em3kAqdhy68yPqGcCPecjFc92pMPmLAMPA2P7AV9L9M1DrJTV3rMNEtHXOgXKa2NC-JLSGz3SUVcx29-WN9BSJthJyP27fU8/s1600/f-ratio2.png" height="310" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="color: orange; font-family: Arial, Helvetica, sans-serif; font-size: small;">Relative illumination with increasing focal length</span></td></tr>
</tbody></table>
<span style="font-family: Arial, Helvetica, sans-serif;"><i>So if we have a fixed aperture of 200mm and a focal length of 400mm, we have an f/2 system. Increasing the focal length to 800mm gives us f/4</i></span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;">In this case the relationship is that if you <u>double the focal length</u>, you get a <u>quarter of the illumination</u>. Again, it's a simple matter of geometry as you can see from the illustration below:</span></span><br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhQ1kcH7SlE4FnmLEnRyHwGwrtqCeMH2WWBpj6LIJDcvub4tdN2GDCoRNmNdpEo3_7NpnQmh91srdstQZx62hwdRWmTwreIDLwSA1f78D18RTHs8Z3F2vFqnNOCANIxN3ebOLGahIFB9BA/s1600/focal+length.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhQ1kcH7SlE4FnmLEnRyHwGwrtqCeMH2WWBpj6LIJDcvub4tdN2GDCoRNmNdpEo3_7NpnQmh91srdstQZx62hwdRWmTwreIDLwSA1f78D18RTHs8Z3F2vFqnNOCANIxN3ebOLGahIFB9BA/s1600/focal+length.png" height="251" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="color: orange; font-family: Arial, Helvetica, sans-serif; font-size: small;">Effect of increasing focal length</span></td></tr>
</tbody></table>
<span style="font-family: Arial, Helvetica, sans-serif;">We're imaging objects that are at infinity, so doubling the focal length of your scope or lens will also double the "magnification". An image of a straight line line that is 1mm long on the the camera sensor at a focal length of 500mm would be 2mm long if you increased the focal length to 1,000mm (left hand side of the illustration above).</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;">
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span><span style="font-family: Arial, Helvetica, sans-serif;">But we are concerned about how much light falls in an <u>area</u>. So if </span><span style="font-family: Arial, Helvetica, sans-serif;">100% of the incoming light falls in a box of 1mm x 1mm = 1mm<sup>2</sup> at a focal length of 500mm, then it will fall in a box of </span><span style="font-family: Arial, Helvetica, sans-serif;">2mm x 2mm = 4mm<sup>2</sup> at a focal length of 1,000mm (middle of the illustration).</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;">So at 1,000mm focal length we have the same amount of light falling in 4 x 1mm<sup>2</sup> boxes, which means that a <u>quarter</u> of the light falls in each of the 1mm<sup>2</sup> boxes as fell in the original 1mm<sup>2</sup> box at 500mm focal length (right hand side of the illustration).</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;">In the real world the boxes that we are concerned about are the pixels on our camera sensor. <u>By doubling the focal length, we put one quarter as much of the incoming light on each pixel.</u></span><br />
<br />
<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;">Note 1: We aren't really imaging objects that are infinitely far away, but they are as close to infinity as makes no practical difference to the optics of your telescope or lens.</span></b></span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;">Note 2: Fitting an image of a galaxy that is hundreds of thousands of light years across on to a sensor that is 20 or 30mm across hardly counts as magnification! When we use the term "magnification" in this context, we should really say that we are increasing the apparent <a href="http://en.wikipedia.org/wiki/Angular_distance" target="_blank">angular separation</a> of features in the image.</span></b></span></span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;">There is an important rider on focal length, in that it breaks down when we start dealing with <a href="http://en.wikipedia.org/wiki/Point_source#Light" target="_blank">Point Sources</a>. A point source is anything which:</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;">- Has an angular size that too small to be <a href="http://en.wikipedia.org/wiki/Angular_resolution" target="_blank">Resolved</a> by your telescope; <u>stars</u> most certainly fit this definition.</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;">- Is resolved by your telescope but not by your camera due to large sensor pixels or a short focal length, i.e. the light from the object falls entirely on to a single camera pixel. (We'll come back to this in Part 2).</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<b><span style="font-family: Arial, Helvetica, sans-serif;">In the case of a point source, focal length has no relevance; the brightness of the object at the camera sensor is determined </span><span style="font-family: Arial, Helvetica, sans-serif;">entirely</span><span style="font-family: Arial, Helvetica, sans-serif;"> </span><span style="font-family: Arial, Helvetica, sans-serif;">by the aperture of the scope. In other words, you can't make it any brighter by reducing the focal length (thus reducing the "magnification") - it's already as small as it can be.</span></b><br />
<br />
<h3>
<span style="font-family: Arial, Helvetica, sans-serif;">
<b style="font-family: Arial, Helvetica, sans-serif;">All f-ratios are not created equal</b></span></h3>
<span style="font-family: Arial, Helvetica, sans-serif;">
<br />
<span style="font-family: Arial, Helvetica, sans-serif;">The observant amongst you will have noticed that the two methods of changing f-ratio have very different consequences. Increasing aperture leads to a lower ("faster") f-ratio by gathering more light, whereas reducing focal length does the same by shrinking the image and thus concentrating the same amount of light on to a smaller area.</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;"><i>So a 200mm aperture / 2,000mm focal length telescope and a 100mm aperture / 1,000mm focal length telescope are both f/10. The former will gather four times as many photons as the latter in the same amount of time, but it will also spread them out over an area that is four times as large. If we use the same camera on both telescopes, the sensor pixels will receive the same number of photons in each case.</i></span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;">So that means one f/10 scope is just as good as another, right? Not necessarily:</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;">-<b> Firstly, the shorter focal length instrument will project a half-sized image on to your camera sensor, and thus the resulting image of the target will consist of a quarter as many pixels. Whether this matters or not depends on the size of your camera pixels.</b></span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;"><b>- Secondly, the quality of your image may be better or worse depending on the brightness of your target, the brightness of the sky and the amount of read noise produced by your camera.</b></span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;">We'll examine these issues in more detail in Part 2 of this series before drawing some conclusions.</span></span></div>
Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4541271552202931674.post-27689200665580929722014-03-02T17:03:00.002+00:002014-10-16T15:31:23.775+01:00SpongeBob where are you?<span style="font-family: Arial, Helvetica, sans-serif;">The Jellyfish Nebula (IC443), the remains of a supernova in the constellation of Gemini. It is about 5,000 light years away and was created sometime between 3 and 30 thousand years ago. Also top centre is IC444 which is a blue nebula due to starlight being reflected off gas and dust. (No sign of SpongeBob or Patrick though). Seeing was particularly good on this night.</span><br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhExnVRFpqodZQuACiHnhvJUf3yMXLHiFgMP94-9SJILb0yzGtUPa-hRicbswS-r6nti7mcjaghp9Zdbv460MPDODIAQs4fh1Y8Wv3ccOKrDL2ByqNYRzL1fnmnQDsWMMrZgzDX2G0RDQw/s1600/Jellyfish_Nebula_3x.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhExnVRFpqodZQuACiHnhvJUf3yMXLHiFgMP94-9SJILb0yzGtUPa-hRicbswS-r6nti7mcjaghp9Zdbv460MPDODIAQs4fh1Y8Wv3ccOKrDL2ByqNYRzL1fnmnQDsWMMrZgzDX2G0RDQw/s1600/Jellyfish_Nebula_3x.png" height="420" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="color: orange; font-family: Arial, Helvetica, sans-serif; font-size: small;">IC443 and IC444</span></td></tr>
</tbody></table>
<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;">Imager:</span></b> Sky-Watcher Evostar 80ED DS-Pro, </span><span style="font-family: Arial, Helvetica, sans-serif;">Sky-Watcher 0.85x Focal Reducer, </span><span style="font-family: Arial, Helvetica, sans-serif;">Canon EOS 500D (Unmodified), </span><span style="font-family: Arial, Helvetica, sans-serif;">Hutech IDAS LPS P2 2", </span><span style="font-family: Arial, Helvetica, sans-serif;">APT - Astro Photography Tool</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;">Guider:</span></b> Orion ST80,</span><span style="font-family: Arial, Helvetica, sans-serif;"> QHY 5, PHD Guiding</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;">Mount:</span></b> Sky-Watcher NEQ6, </span><span style="font-family: Arial, Helvetica, sans-serif;"> AstroTortilla, EQMod</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;">Processing:</span></b> PixInsight 1.8</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;">Dates:</span></b> March 1st, 2014</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;">LIghts:</span></b> 13 x 600seconds ISO400 (</span><span style="font-family: Arial, Helvetica, sans-serif;">2.2 hours)</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;">Darks:</span></b> 109</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;">Flats:</span></b> 102</span><br />
<b style="font-family: Arial, Helvetica, sans-serif;"><span style="color: orange;">Bias:</span></b><span style="font-family: Arial, Helvetica, sans-serif;"> 330</span>Unknownnoreply@blogger.com1tag:blogger.com,1999:blog-4541271552202931674.post-86867534256154463182014-01-25T15:37:00.002+00:002014-02-05T12:16:00.780+00:00M101 Widefield<span style="font-family: Arial, Helvetica, sans-serif;">This image was taken on my first night out following the street light switch-off in the nearby towns (between midnight and 5:00am), helpfully the moon was also on the opposite side of the sky by this time. As you can see, I have also also managed to capture a fair few of M101's companion galaxies in this image, including NGC5474 just left of top centre.</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<br />
<div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgtSEd78A5Uc7xXk40yt_Mesx5lxDH7vuBGhps6P3T3rogwxVctbwQSyD_0Dj_DXmX8DgjJIKoRw88W4mT4xCxWy3T_CPgIHtoTX2YHTWwKrPeke6GeQ_2NJ7QtXLDOyEjmqgMH7yXJvzc/s1600/M101_V1_3x.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><span style="font-family: Arial, Helvetica, sans-serif;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgtSEd78A5Uc7xXk40yt_Mesx5lxDH7vuBGhps6P3T3rogwxVctbwQSyD_0Dj_DXmX8DgjJIKoRw88W4mT4xCxWy3T_CPgIHtoTX2YHTWwKrPeke6GeQ_2NJ7QtXLDOyEjmqgMH7yXJvzc/s1600/M101_V1_3x.png" height="425" width="640" /></span></a></div>
<br />
<span style="font-family: Arial, Helvetica, sans-serif;"></span><br />
<a name='more'></a><span style="font-family: Arial, Helvetica, sans-serif;">This is also the first image I have processed using PixInsight's new 'Masked Stretch' process (released this week, replacing the old script version). It has made a massive difference to retaining colour in the cores of the stars and the galaxy, so much so that I may well have to go back and reprocess some of my earlier images which suffer from a lack of star colour (a common problem with DSLR images).</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;">Imaging:</span></b> Sky-Watcher Evostar 80ED DS-Pro, Sky-Watcher 0.85x reducer, Hutech IDAS LPS P2 2", Canon EOS 500D (Unmodified), APT </span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;">Guiding:</span></b> Orion ST80, QHY 5, PHD guiding, Sky-Watcher NEQ6, EQMod, AstroTortilla</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;">Processing:</span></b> PixInsight 1.8.01</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;">Date:</span></b> Jan. 12, 2014</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;">Lights:</span></b> 30 x 600 seconds ISO400</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;">Darks:</span></b> 109</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;">Flats:</span></b> 102</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;">Bias:</span></b> 330</span><br />
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<br />Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-4541271552202931674.post-4420168242307664242014-01-19T12:42:00.000+00:002014-02-05T12:15:48.224+00:00M42 plus M43 - Unmodded DSLR Image<span style="font-family: Arial, Helvetica, sans-serif;">M42 - The Orion Nebula, plus top left M43 - De Marian's Nebula (aka "The Running Man Nebula"). This is 30 x 30 second exposures, plus 22 x 320 second exposures in an HDR composite, taken 11th Jan 2014.</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<span style="font-family: Arial, Helvetica, sans-serif;">Again I was battling a nearly full Moon as we seem to get nothing but rain around here when the skies are fully dark! This image was processed entirely in PixInsight. I hope to get some longer exposures to try to capture more of the surrounding dust.</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><br /></span>
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh4AMIVBjeDyBrvM-bOwgppOy3HjA4w0RHu8xmztJXqTBbzSuI-_DiGsQzaGCUrVkiEOjqGPfrquSWznxJR5M5sIFFxc08V84-iOQg6ym_z2iyOiN_aZoGX2z7NV2AmG5ag9oWSjFGabs8/s1600/M42_v1_2x.png" imageanchor="1"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh4AMIVBjeDyBrvM-bOwgppOy3HjA4w0RHu8xmztJXqTBbzSuI-_DiGsQzaGCUrVkiEOjqGPfrquSWznxJR5M5sIFFxc08V84-iOQg6ym_z2iyOiN_aZoGX2z7NV2AmG5ag9oWSjFGabs8/s640/M42_v1_2x.png" height="469" width="640" /></a><br />
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<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;">Imaging:</span></b> Sky-Watcher Evostar 80ED DS-Pro + </span><span style="font-family: Arial, Helvetica, sans-serif;">0.85x, </span><span style="font-family: Arial, Helvetica, sans-serif;">Canon EOS 500D (Unmodified), </span><span style="font-family: Arial, Helvetica, sans-serif;"> </span><span style="font-family: Arial, Helvetica, sans-serif;">Hutech IDAS LPS P2, </span><span style="font-family: Arial, Helvetica, sans-serif;">APT - Astro Photography Tool</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;">Mount:</span></b> Sky-Watcher NEQ6</span><span style="font-family: Arial, Helvetica, sans-serif;">, AstroTortilla, EQMod</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;">Guiding:</span></b> Orion ST80, </span><span style="font-family: Arial, Helvetica, sans-serif;">QHY 5, </span><span style="font-family: Arial, Helvetica, sans-serif;">PHD guiding</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;">Processing:</span></b> PixInsight</span><br />
<span style="color: orange; font-family: Arial, Helvetica, sans-serif;"><b>Subs:</b></span><span style="font-family: Arial, Helvetica, sans-serif;"> 30 x 30 seconds, 22 x 320 seconds, ISO 400</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;">Date:</span></b> Jan. 11, 2014</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;">Darks:</span></b> 109</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;">Flats:</span></b> 102</span><br />
<span style="font-family: Arial, Helvetica, sans-serif;"><span style="color: orange;"><b>Bias:</b></span> 330</span>Unknownnoreply@blogger.com1tag:blogger.com,1999:blog-4541271552202931674.post-30419887843876758502014-01-08T13:54:00.002+00:002014-02-05T12:15:04.465+00:00Do High ISOs Make DSLRs More Sensitive To Light?<span style="font-family: Arial, Helvetica, sans-serif;">Many new astro-imagers believe that they can make their camera more sensitive to light by using a higher ISO setting. This is not surprising given that there are a vast number of articles out there that continue to spread this myth (including photography magazines and other technical publications that really ought to know better).</span><br />
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<span style="font-family: Arial, Helvetica, sans-serif;">After yet another <a href="http://www.bbc.co.uk/science/0/25401782" style="font-family: Arial, Helvetica, sans-serif;" target="_blank">misleading write-up</a>, this time from the BBC promoted by Stargazing Live (no less!), I thought I'd do my best to set out a few facts which will help you to understand what is really going on and therefore to take better images. </span><span style="font-family: Arial, Helvetica, sans-serif;">Read on for more.</span><br />
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<span style="font-family: Arial, Helvetica, sans-serif; font-size: large;"><b>The Truth About ISO</b></span><span style="font-family: Arial, Helvetica, sans-serif;"><br /></span><br />
<span style="font-family: Arial, Helvetica, sans-serif;">The simple fact is that using a higher ISO does <u>not</u> make your camera's digital sensor more sensitive to light. Read that sentence again and memorise it. Anyone who tries to convince you otherwise is just plain wrong and I'll explain why.</span><br />
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<span style="font-family: Arial, Helvetica, sans-serif;"><a href="http://en.wikipedia.org/wiki/Film_speed" target="_blank">ISO numbers</a> are a standardised system of measurement of film sensitivity from the pre-digital era, where they did indeed indicate physical differences in the sensitivity of various film emulsions to light. Perhaps unfortunately, the concept was carried forward to digital photography as a sales/marketing tool to sell to a customer base transitioning from film to digital photography.</span><br />
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<span style="color: orange; font-family: Arial, Helvetica, sans-serif;"><b>In truth, ISO numbers have no fundamental basis in the way digital sensors work.</b><br />
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<span style="font-family: Arial, Helvetica, sans-serif; font-size: large;"><b>Quantum Efficiency Is Where It's At</b></span><span style="font-family: Arial, Helvetica, sans-serif;"><br /></span><br />
<span style="font-family: Arial, Helvetica, sans-serif;">A CMOS (or CCD) sensor has what is known as a <a href="http://en.wikipedia.org/wiki/Quantum_efficiency" style="font-family: Arial, Helvetica, sans-serif;" target="_blank">Quantum Efficiency</a> (QE) which is the percentage of incoming photons of light that are converted in to electrons that can then be measured and converted to an image. A perfect sensor would have a QE of 100% at all wavelengths of light so that every incoming photon is detected and turned in to a measurable electron. In reality all sensors have a QE that is much lower than 100%, and the QE will also vary by wavelength.</span><br />
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<span style="font-family: Arial, Helvetica, sans-serif;">A typical monochrome CCD sensor might have a QE of 40% at the blue end of the visible spectrum rising to perhaps 60 or 70% at the red and near infra-red end, whereas a typical (unmodified) DSLR sensor will have an (effective) QE of perhaps 40% for the pixels with the blue and green <a href="http://en.wikipedia.org/wiki/Bayer_filter" target="_blank">Bayer filters</a> and maybe 30% for the red ones. So as a DSLR user, <u>much less than half</u> of the incoming light is going to be recorded in your image.</span><br />
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<span style="font-family: Arial, Helvetica, sans-serif;">The lack of sensitivity at the red end is a further problem for DSLRs as it blocks most of the useful Hydrogen Alpha wavelength from emission nebulae, but it can be improved by removing or changing the infra-red cut filter which is put on top of the whole sensor. That infra-red filter is useful for daylight photographers as it produces more natural looking images out of the box as well as avoiding problems with blurry images or poor contrast caused by out-of focus infra-red light falling on the sensor.</span><br />
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<span style="font-family: Arial, Helvetica, sans-serif;">There are many articles out there describing how to modify your camera to replace the infra-red filter for one that performs better in this regard. It is not a simple process, so if you're not willing to risk breaking your camera, you can also buy ready-modified cameras from some suppliers at a reasonable price, or direct from Canon (the 60Da) at a much less reasonable price. The results will be much better on emission nebulae, but still not as high a QE as a typical monochrome CCD.</span><span style="font-family: Arial, Helvetica, sans-serif;"><br />
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<span style="font-family: Arial, Helvetica, sans-serif; font-size: large;"><b>Myth Busted</b></span><span style="font-family: Arial, Helvetica, sans-serif;"><br /></span><br />
<span style="font-family: Arial, Helvetica, sans-serif;">The important point is that each sensor pixel <u>has a QE that was fixed at the point it was manufactured</u>, and indeed the QE varies from pixel to pixel due to manufacturing imperfections. That QE will be further reduced when you put a filter in front of it (whether that is an interchangeable filter for a mono CCD or the fixed Bayer pattern filter in a DSLR).</span><br />
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<span style="font-family: Arial, Helvetica, sans-serif;"><i>Strictly speaking, the QE of the sensor pixel is the same, but the <u>effective</u> QE reduces since the filter blocks some of the photons before they get to the sensor.</i></span><br />
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<span style="font-family: Arial, Helvetica, sans-serif;"><b><span style="color: orange;">The important point is that there is no setting on the camera which changes the underlying QE of the sensor elements. The same percentage of photons falling on the pixel will be converted to electrons regardless of any ISO (or gain) setting.</span></b></span><br />
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<span style="font-family: Arial, Helvetica, sans-serif;">In the digital imaging world, ISO is just a different way of expressing 'gain'. Gain is simply the amount of amplification that is applied to the electrons in each pixel's electron well prior to converting the measured voltage to a number in the analog to digital convertor (ADC) on the sensor. Increase the gain (amplification) and a bigger number comes out of the A/D converter, which results in a 'brighter' image on the screen.</span><br />
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<span style="font-family: Arial, Helvetica, sans-serif;">The marketing and product development bods decided to describe the camera's gain settings using the existing system of ISO numbers that their target market were already comfortable with as previously discussed. Hopefully you now understand that ISO in digital cameras has no bearing on their sensitivity to light.</span><br />
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<span style="font-family: Arial, Helvetica, sans-serif;"><i>As an aside, whilst the gain settings are designed to mimic the sensitivity increments of film ISO numbers, there is no absolute fixed reference point. One sensor's ISO 100 is not (necessarily) the same as another sensor's ISO 100. In any case, neither is a reflection of the true sensitivity of the sensor just that 'brightness' of the resulting image is <u>similar</u> to that of using ISO 100 film on the same scene.</i><br />
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<span style="font-family: Arial, Helvetica, sans-serif; font-size: large;"><b>Is Bigger Really Better?</b></span><span style="font-family: Arial, Helvetica, sans-serif;"><br /></span><br />
<span style="font-family: Arial, Helvetica, sans-serif;">Of course the marketing people realised that people always buy on the basis of the biggest numbers, so 'ISO wars' broke out. Everyone wants a bigger speedboat than the neighbours, and they also want a camera that offers ISO 25600 instead of one that only goes up to ISO 3200 or ISO 6400! In reality those really high ISOs are simply pointless multiplication of the digital values <u>after</u> the useful ADC process.</span><br />
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<span style="font-family: Arial, Helvetica, sans-serif;">The cut off between amplifier gain and digital multiplication is usually somewhere in the region of ISO 1600 or ISO 3200, again your mileage will vary with model. This latter process (for astro-imagers) is not at all useful since you can stretch the <a href="http://www.blackwaterskies.co.uk/2013/12/how-to-interpret-image-histogram.html">image histogram</a> in your image processing software to achieve the same result and do it with far more control as we'll see below.<br />
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<span style="font-family: Arial, Helvetica, sans-serif; font-size: large;"><b>Still Not Convinced?</b></span><span style="font-family: Arial, Helvetica, sans-serif;"><br /></span><br />
<span style="font-family: Arial, Helvetica, sans-serif;">If you look at an dedicated astronomical CCD camera, it does not have an ISO setting. It will either have a factory-fixed gain setting to give the best signal-to-noise ratio, or a user configurable gain setting which will just be some arbitrary range of numbers that makes sense to the camera/capture software creators (in which case you'll be expected to perform tests to figure out the best gain setting for your requirements).</span><br />
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<span style="font-family: Arial, Helvetica, sans-serif;">Furthermore, if you look at your mobile phone, webcam or low-end digital camera it doesn't have an ISO setting even though it will have the same sort of CMOS or CCD sensor as a DSLR. At best you'll have a brightness and contrast setting which are used to manipulate both the sensor gain and the image histogram simultaneously in a way that is familiar to people who remember analogue TVs.</span><br />
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<span style="font-family: Arial, Helvetica, sans-serif;"><i>Again, contrast and brightness are just concepts carried over from the world of analogue TV for familiarity's sake (both in the webcam and digital TV worlds)!</i></span><br />
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<span style="font-family: Arial, Helvetica, sans-serif;">Indeed with a typical mobile phone or point and shoot camera, the device itself will try to absolve you or all responsibility by analysing the image and coming up with the best settings it can untouched by human hand.<br />
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<span style="font-family: Arial, Helvetica, sans-serif; font-size: large;"><b>So What ISO Should You Use?</b></span><span style="font-family: Arial, Helvetica, sans-serif;"><br /></span><br />
<span style="font-family: Arial, Helvetica, sans-serif;">You should use an ISO setting which satisfies two key objectives:<br />
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<li><span style="font-family: Arial, Helvetica, sans-serif;">Start with an ISO that is as close to 'Unity Gain' for your camera as possible (but never less than 1 electron = 1 ADU). This will ensure that you don't unnecessarily convert different voltages from the sensor pixels to the same brightness level in the final image. Unity Gain is the amplification setting that converts exactly one electron from a sensor pixel to one ADU (number) in the image file (I have covered ADUs before <a href="http://www.blackwaterskies.co.uk/2013/12/how-to-interpret-image-histogram.html" style="font-weight: normal;" target="_blank">here</a>). For Canon cameras Unity Gain is likely to be somewhere in the region of ISO 200 or 400. You will need to perform tests to figure this out for each specific camera model and there is unlikely to be an ISO value that is exactly Unity, so go for the nearest that is above 1.</span></li>
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<li><span style="font-family: Arial, Helvetica, sans-serif;">Some ISO settings may produce a better signal to noise ratio than other ISO settings, so it <u>might</u> make sense to use an ISO which is higher (but rarely lower) than the one which approximates Unity Gain. The higher voltage coming out of the amplifier may result in less read-out noise and again your mileage will vary depending on the camera model.</span></li>
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<span style="font-family: Arial, Helvetica, sans-serif;">Craig Stark describes how to determine the best ISO setting for your particular DSLR in his article </span><a href="http://www.cloudynights.com/item.php?item_id=2786" style="font-family: Arial, Helvetica, sans-serif;" target="_blank">Profiling the Long-Exposure Performance of a Canon DSLR</a><span style="font-family: Arial, Helvetica, sans-serif;">. His advice (and mine based on practical experience) is that low ISOs are better for astro-imagers. I generally shoot at ISO400 using my Canon 500D.</span><br />
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<span style="font-family: Arial, Helvetica, sans-serif; font-size: large;"><b>But If I Use A Low ISO, My Images Are Too Dark!</b></span><span style="font-family: Arial, Helvetica, sans-serif;"><br /></span><br />
<span style="font-family: Arial, Helvetica, sans-serif;">Now to be fair to the BBC article I linked at the top of this piece, there is sometimes a good reason for (beginning) astro-imagers to use a much higher ISO than my advice suggests. If you are shooting using just the camera (with no laptop to control it) then you will have to rely on the tiny display screen on the back of the camera to preview and check your images. Using a low ISO may render the image hard to see or invisible, and you probably shouldn't wait until you get indoors to check your results so you may have to use a higher-than-ideal ISO.</span><br />
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<span style="font-family: Arial, Helvetica, sans-serif;">My problem with the article (and so many others) is that it doesn't say that, it specifically says "A higher ISO number means more sensitivity...". This leaves beginners with a misconception that stays with them for a very long time afterwards, and causes many to make fundamental mistakes in their imaging techniques once they become more advanced.</span><br />
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<span style="font-family: Arial, Helvetica, sans-serif;">Depending on your target and exposure time, an image taken at a low ISO may well be dark, but that is not the same thing as saying that a dark image contains less information than a bright image (indeed the opposite is far more likely as we discussed above). It is just that you will need to do a bit more work to make it visible.</span></div>
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<span style="font-family: Arial, Helvetica, sans-serif;">The solution to an image that is too dark is to stretch the histogram using an image processing package:<br />
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<li><span style="font-family: Arial, Helvetica, sans-serif;">Most DSLR manufacturers supply software for converting their RAW images to other formats, and as part of the process you can usually adjust the histogram to make the image brighter. This may not be the best approach however.</span></li>
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<li><span style="font-family: Arial, Helvetica, sans-serif;">A better solution is to bring the RAW image straight in to your photo-processing or astro-image processing software (e.g. PhotoShop, PixInsight, Deep Sky Stacker, etc.), all of which have tools for manipulating the histogram to make the image brighter. This will ensure that you start out with the maximum amount of detail in the image and have full control over how it is manipulated.</span></li>
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<li><span style="font-family: Arial, Helvetica, sans-serif;">The processes in the various packages have different names such as <a href="http://en.wikipedia.org/wiki/Histogram_equalization" target="_blank">Histogram Equalisation</a>, Curves, Histogram Transformation, Brightness and Contrast, etc. In all cases, the software can make a seemingly 'black' and very unpromising astro-image reveal the hidden glory of stars, galaxies and nebulae.</span></li>
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<i style="font-family: Arial, Helvetica, sans-serif;">In saying all this, I've assumed that you are shooting RAW images with your DSLR rather than JPEG images. If you aren't, please change your settings now! JPEG images throw away a lot valuable detail in an image (both in terms of brightness levels and resolution). As an astro-imager you should always shoot RAW images and only ever convert them to JPEG or other web-friendly formats at the very end of processing.</i><br />
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<span style="font-family: Arial, Helvetica, sans-serif; font-size: large;"><b>The Bottom Line</b></span><span style="font-family: Arial, Helvetica, sans-serif;"><br /></span><br />
<span style="font-family: Arial, Helvetica, sans-serif;">As an astro-imager, really you need to focus on gain (through the imperfect medium of ISO numbers for DSLR users) and histogram transfer functions (in post-processing) to avoid misunderstanding what it is you are really doing when creating or processing an image.</span>Unknownnoreply@blogger.com0