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Originally Posted by Garbz
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Screenshot of the master flat with an AutoSTF is attached. It's the one of the left. Yes OSC camera. All batch pre-processing. Most values are left at default except that I use overscan correction, master dark and master bias frames. I typically do integration outside of the script and use it to calibrate debeyer and register only, but it's not an integration problem the result is the same regardless of if I use the script or not.
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You just gave me an idea. I've attached an example with master on the left, original in the centre, and calibrated with the heck stretched out of it on the right. The result shows some problem to the left of the frame but no real issue with vignetting or dust spots. I've calibrated all flats and all showed the same kind of response as the right most image. This could point to a problem with either the darks or the bias frames. I'll do a bit more digging. But what is absent from this picture is problems of vignetting and dust motes which are an issue for the main image.
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I don't know of many people that use overscan other than Rick. I don't know if or how he does flat calibration, but if he does, then he clearly isn't having this same issue or he'd have mentioned it.
I did have a play some time ago with overscan, and I have in the past had a similar issue with flats not correcting properly. It was so long ago that I don't recall if the flats issue was happening while I was testing overscan. I've since stopped using overscan as it wasn't benefiting my images appreciably.
What I'm getting at - perhaps try some bias, dark, light, flat files without the overscan to see if you still have the issue there? Just to rule it out.