The stuff by Richard Crisp is here:
http://www.narrowbandimaging.com/flat_fielding_page.htm
It's not easy reading for the new or faint-hearted
Quote:
Originally Posted by solissydney
ADU's ????????
What?
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ADU = analog-digital unit. When your image analysis program tells you that the value in a pixel is 10456 then that's measured in ADUs. The other measure that is used is the number of electrons captured. The number of electrons is scaled by a gain factor to give ADUs. The gain factor varies depending on the characteristics of the camera sensor.
Ideally you want your flats to have a high average ADU count without going so high that you stray into the non-linear area of your CCD's performance curve. There isn't a specific formula for this because it will depend on your sensor. The usual advice is to target around 20,000 to 30,000 ADU. Richard Crisp's stuff talks about how many flat frames are needed to reduce flat-fielding noise to an appropriate level.
Cheers,
Rick.