Flats- Exposure lengths

[Zakalwe]

A quick question...Does the exposure length for flats matter? Say I am taking flats binning 2x2 (for RGB filters) then does it matter if the exposure length in something like .05 seconds? At that length I would assume that read-out noise (bias) is in the flat?

Would a longer exposure be better or does it not matter at all, as long as the ADU value is around 25K?

Thanks in advance.

[johnrt]

Exposure length doesn't matter just aim for the 23-25k mark, then bias subtract your flats before you combine in to a master.

[Zakalwe]

Thanks Johnrt, much appreciated.

[ollypenrice]

This is true if your camera doesn't have a shutter (which usually means 'if it doesn't use the 8300 chip.') If it does, then the shutter dawdling across the frame will wipe a nasty gradient onto the flats. You need to make flats with shutters expose for a few seconds to reduce this to an insignificant level.

Ollly