|
If you have a mechanical shutter going too short will give you shadows. If your camera has high dark current then you don't want to go for very long flats. Otherwise, I can't think of any reason to prefer duller/longer or brighter/shorter.
To minimise the noise added by flat calibration you probably want to collect a total of a couple of hundred electrons in total. I usually target 500Ke- but that's easy to do with deep wells - only a dozen flats.
|