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If your taking new Flats for each session or project then you should be taking matching Flat Darks or Dark Flats ( same exposure, Gain and temperature)
Bias frames are sometimes used to calibrate Flats but only when Flats exposure times are under 1 sec as the resultant stacked Master Flat dark current is almost zero. In addition using Bias frames to calibrate Flats may not totally eliminate hot and cold pixels as well as Amp Glow which is common on a lot of mid range CMOS cameras.
Using Flat Darks in all cases are a safe measure to calibrate your Flats as dark current in cameras is either an unknown quantity or known quantity and can vary ( each camera has its own signature) They are the “Gold Standard” when it comes to calibrating Flats.
Believe it or not ,the high end Sony IMX571 sensor used in the 2600MC and 2600MM still exhibits hot pixels and some random telegraph noise. The noise goes down if you apply darks. Secondly the flat correction will not work properly without dark and flat-darks pedestal value. The pixels in the frames have also a natural variation in the pedestal value. Only if you have very poor skies maybe you will not notice in the images.
I take new Flats and Flat Darks for each project and keep a Dark Library for reuse around 9 to 12 months.
Once you master it, taking Flats and Flat Darks is easy and not time consuming.
A full calibration suite should not be a “Chore” and it will definitely improve your images. I’m my case I have no choice as I have severe vignetting in any case.
Martin
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