I should add that some software will use bias frames as flat darks. But that is not common. If the software asks for flat darks and you don't give it any, your flats will not be applied correctly and will have less than the intended effect.
+1 I notice you did not use flat darks.
I am adding the bias frames to the flats, per Craig Stark's instructions.
You don't need dark flats if the flat exposures are short, (which they are - 1/30th second, ISO 100). In this case, the bias frame is essentially the dark flat (1/4000th sec, also at ISO 100).
When doing narrow-band work, the flat frames become much longer, so then you need dark flats.
I have tried many combinations so far to see what might be happening. I thought it might be setting (or not setting) the black point to zero, based on the bias frames. But that wasn't it either.
Attached are 4 cases of stacking:
1. lights, darks, flats and bias
2. lights, darks flats (no bias)
3. lights, flats, bias (no darks)
4. lights, flats (no dark, no bias)
5. lights only (no darks, flats or bias)
6. And the most interesting case is when I took the lights-only stacked file, and the master flat, brought it into GIMP (2.9 beta version, 16 bit), and inverted the master flat and made it an addition layer (divide would not work). That is the best so far. But I shouldn't have to so that.
Edited by StevenBellavia, 10 February 2018 - 12:13 PM.