Piers Palmer:
took a bunch of dark frames back in the spring; 30", 60", 120" etc, at the same gain that I use and the same cooling (gain 100, -10ºC) with my ASI2600MC Pro. I took 20 at each setting. Does that relate to your points? I'm not sure what you mean by matching the offset...I'm a bit of a thicko when it comes to this sort of stuff.
Hi Piers. You have matched most things but not everything I think. So no it doesn't..
In the ZWO camera image control menu there is also a setting called 'brightness' . I normally have it set at 10 for example on my ZWO ASI 1294MC -- some folk habitually set at 4. My point is only that the crucial importance of this control sometimes get missed. It is just as important to have this set exactly the same as the rest of the parameters -- a difference of 1 even makes a telling difference-- between darks and lights. When it is wrong the effect is very much as you have seen which is why I suspect that it might be the problem.
So you just need to check what the brightness value was set at (programs like Sharpcap stores a text file that saves this information whenever master darks and autostacks of lights are saved)
Until you have checked this I would not rush to the conclusion that it is anything to do with the flats. Fixing things would then simply entail making another dark at a brightnes ssetting that matches the lights.
PS some discussion here about offset and other settings for your camera, May be useful even if it turns out to be unrelated to your current issue. Maybe ZWO do use the term offset rather than brightness for the 2600 ?
https://www.astrobin.com/forum/c/equipment-forums/zwo-asi2600mc-pro/parameters-for-the-asi2600mc-pro/#
