Quote:
Originally Posted by Shiraz
well, maybe I was a bit premature on that advice - apologies.
just had a look at a bias sub from mine - it has a smattering of dark pixels, but they are not that far from the mean. A typical 21x21 pixel region has a mean of ~290, min of 224, max 352 (bias21, gain 100). That is a range of about 3 sigma, with nothing at very low values, so your camera is behaving somewhat differently. I seem to recall that these cameras can do strange things with very short bias subs - could that be an issue? I went over to 1 second bias subs early on, but do not have any older very short subs to have a look at.
yep, min/max for all stacks seems to work best. For lights, I have been using sparse dither where dither only applies every 3 frames, and have been using rejection of the 4 highest and 4 lowest (all standard normalisation) - seems to do fairly well. not perfect, but the occasional leaked hot pixel is fairly easy to deal with. cheers Ray
edit: just another thought, with short exposures there is so little signal that it is often necessary to add in a pedestal when calibrating to ensure that the data cannot try to go negative when the dark+bias is subtracted. Might be unrelated to your issue, but it can cause odd data distributions.
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Interesting Ray, i have always used 0 sec bias frames when using SGP, because it can. Sounds like i should be using 1 sec bias. My whole 1600 bias library is built on 0 sec subs.
