Help with M81 Colors

[Rowland]

I ran it all manually through Pixinsight - preprocessing only, using my standard DSLR method, plus two other methods. Difficult to say just what the issue is. But as mentioned, 3 methods of processing and same result. I have seen this before, and your dark frames look like there's stray light getting in - probably through the view finder, unless it's covered, of course. The flats won't be affected to the same extent because they are much shorter exposure, but the darks have light areas thoughout - telltale stray light signature, I think. You could throw a fairly heavy pixel rejection at it during preprocessing and see if that improves thing.

EDIT: just read - you are using a CCD. In that case, no idea.

[midwayexpress]

So check this out. This is using the built in bin feature in Startools that I rarely ever touch + 6 more frames using dithering. I would say a drastic improvement.

http://www.astrobin.com/158957/