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Old 08-02-2012, 08:04 PM
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Odd arcs in test image

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?
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Old 08-02-2012, 09:54 PM
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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
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Old 08-02-2012, 10:18 PM
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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.
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Old 08-02-2012, 10:18 PM
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Have you had a good look at the dark frame that you used to calibrate the image?
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Old 09-02-2012, 05:27 AM
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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.
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Old 10-02-2012, 07:08 PM
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That is very strange, not seen that before. I don't think this is a baffle related issue. Very odd.
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Old 10-02-2012, 09:51 PM
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Certainly different, looks a bit like a spider web of sorts, have to agree, never seen that before.

Leon
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Old 11-02-2012, 01:01 AM
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dss arcs

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
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Old 11-02-2012, 10:04 AM
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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.
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Old 13-02-2012, 07:10 PM
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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!
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