Quote: "Now you can set the offset value(increase a little) if you plan to capture bias frame" unquote.
Can you explain to me what exactly you mean here?
Also I have used darkframes with the same exposure time as my light frames, but ended up with a lot of darkspots in my lightframe and even some negative values. I just don't understand how that can even happen. It must have something to do with readout values I would think even though that should be exactly the same in a light frame.
What I have done so far is to add a pedastal (offset) in the lightframes of i.e. 1000adu before I subtract the dark frame to prevent it from going into negative territory.
It then seems to at least get rid of any pattern noise in the image.
Another thing I have wanted to try is to use a somewhat higher gain in my lightframes as opposed to the gain in my darkframes. But those are ofcourse nothing more than "tricks" and that doesn't really solve the problem ofcourse.
The temperature variations that Q talks about, I don't really understand. If I look at 2 hours worth of 10min darkframes, they all have about the same average pixel values with only minor variations, so I doubt that that is the problem.
I will experiment some more with different readout settings and other software to see if that makes any difference.