Odd arcs in test image

[JohnH]

I wonder if anyone can help diagnose the source of the odd bright arcs visible at the top of the attached image?

It was taken with a GSO RC10CF and SGBIG ST2000xm. There was an AP CCDT67 FR in line and a FW fitted with Astronmik filters. I used DSS to calibrate and stack the images.

It does not look like reflections in the FR to me.

Could it be a result of field rotation (my polar alignemnt was not accurate) and processing (I did not do use flats but did use darks)? I do not see these issues in the subs even when pushed hard...

Any ideas?

[LightningNZ]

It's not field rotation. I've never seen anything like it. There are two sets of concentric rings centred top left. It would seem that the fainter one might be a ghost of the 1st. Do you have any light that could be shining back into the scope from a bulleye somewhere?

Cam

[JohnH]

Did a bit more investigation the arcs appear in the Ha and Sii stacks but not in the Oiii. The fainter arcs are from the Ha. Very odd. I think it must be a processing anomoly.

[OzRob]

Have you had a good look at the dark frame that you used to calibrate the image?

[JohnH]

No, but the same darks have been used many times without this issue. Also even with this set the Oiii stack does not show the problem.

[Paul Haese]

That is very strange, not seen that before. I don't think this is a baffle related issue. Very odd.

[leon]

Certainly different, looks a bit like a spider web of sorts, have to agree, never seen that before.

Leon

[sebastion]

i think this maybe from stacking frames that have too much movement between exposures. i have this image from may 09 that was stacked in dss. i cant remember how many frames were taken, but i used a point and shoot that took an image at 5 second intervals. no dark or bias frames and obviously it does not appear in the individual frames. my 2 cents

[gregbradley]

Yeah its got to be some processing artifact. If its not on the subs then it isn't the scope.

How did you align/stack the subs?

Greg.

[JohnH]

Sebastion - thanks - that nailed it. Not sure what I did wrong on first pass but re-stacking has made the issue go away...interesting shot there - it looks a bit like the lighthouse buildings on Montague island....and never thought of trying handheld AP - very creative!