Last night I did my first images ever of the Horsehead and Flame Nebulas. Due to various equipment and weather issues, the total time on target was way too short--only about 24 minutes before a meridian flip and 56 minutes after the meridian flip. Clearly, I'll have to take another run at Horsehead/Flame.
Still, a few subs are better than none. Tonight I processed he before-flip and after-flip images separately. Cropped pics showing just Alnitak and part of the Flame Nebula are below.
In the after-flip image, there are pronounced and asymmetrical artifacts around Alnitak--they look to me like curved diffraction spikes. Although the imaging train was exactly the same, these spikes are absent in the before-flip image. I realize, of course, that processing has resulted in different colors, contrast and black point in the two pictures, and the scale of the two images as cropped by me isn't exactly the same, but the difference is also plainly visible in the unprocessed subs.
Can somebody help me figure out why these spikes are present in the after-flip image and not the before-flip image?
Image train: 120mm f/7.5 Refractor--->Baader UV/IR Cut filter--->Celestron OAG--->ASI294 MC Pro Camera
If it might be germane to the issue, the temperature was dropping gradually--maybe 4 degrees F in total--through these two sequences. And I stopped imaging when a cloud got between me and the target.
Before the flip:
After the flip: