When I capture flat frames, combinations of illumination level and exposure that result in proper a proper histogram, also result in horizontal lines across the frame. I rotated the source and the lines don't move. Generally exposures that yield a histogram over 2/3 show no visible lines.
Many sources say to use the gain used on the light frames, but your guidance says 0 gain. I have tried it both ways.
Celestron C8
f10 & f6.3
ASI294 color
Spike a flat light box
