Lester
22-01-2012, 12:36 PM
Hi all,
as comet Lovejoy fades I want to find out how faint my camera, (modded/cooled Canon 40D) can go. Last night I tried 3,4 and 5 minute exposures at ISO 1600. The 5 minute exposures was beginning to fog in the dark areas, but the tail was still improving in contrast over the sky background. So some sky fog is okay, but how much.
Will try 6,7 and 8 minute exposures tonight to see when the sky fog over powers the faint tail.
If anyone has done such tests even with CCDs I would be interested to know your findings also.
Here are full size crops of the comet head. Only 1 exposure in each case without any noise reduction. The 400 ISO is the smoothest, but a stack of all exposures is the best. I have tried to process these the same with curves and levels to keep the histogram similar in all cases.
3 minute exposure ISO 1600.
http://i638.photobucket.com/albums/uu109/Lester_045/Comet%20images/77c5f874.jpg
4 minute esposure ISO 1600
http://i638.photobucket.com/albums/uu109/Lester_045/Comet%20images/1325a307.jpg
5 minute exposure ISO 1600
http://i638.photobucket.com/albums/uu109/Lester_045/Comet%20images/d0687e0f.jpg
12 minute exposure ISO 400
http://i638.photobucket.com/albums/uu109/Lester_045/Comet%20images/74cc1ac5.jpg
Stack of all 21 exposures
http://i638.photobucket.com/albums/uu109/Lester_045/Comet%20images/ab491966.jpg
as comet Lovejoy fades I want to find out how faint my camera, (modded/cooled Canon 40D) can go. Last night I tried 3,4 and 5 minute exposures at ISO 1600. The 5 minute exposures was beginning to fog in the dark areas, but the tail was still improving in contrast over the sky background. So some sky fog is okay, but how much.
Will try 6,7 and 8 minute exposures tonight to see when the sky fog over powers the faint tail.
If anyone has done such tests even with CCDs I would be interested to know your findings also.
Here are full size crops of the comet head. Only 1 exposure in each case without any noise reduction. The 400 ISO is the smoothest, but a stack of all exposures is the best. I have tried to process these the same with curves and levels to keep the histogram similar in all cases.
3 minute exposure ISO 1600.
http://i638.photobucket.com/albums/uu109/Lester_045/Comet%20images/77c5f874.jpg
4 minute esposure ISO 1600
http://i638.photobucket.com/albums/uu109/Lester_045/Comet%20images/1325a307.jpg
5 minute exposure ISO 1600
http://i638.photobucket.com/albums/uu109/Lester_045/Comet%20images/d0687e0f.jpg
12 minute exposure ISO 400
http://i638.photobucket.com/albums/uu109/Lester_045/Comet%20images/74cc1ac5.jpg
Stack of all 21 exposures
http://i638.photobucket.com/albums/uu109/Lester_045/Comet%20images/ab491966.jpg