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Hi chaps

Am I right in thinking this might be internal reflections from my filters?

The bright stars all display offset halos. The imaging scope was a WO FLT-110 with Tru-tek filter wheel, Astronomik Ha filter (the wider band one) only used. Camera was Starlight Xpress SXV-H9.

Total exposure in the stack was about 2.5 hours. Imaged from light polluted Rickmansworth/Herts on sat/sun night.

Any explanations gratefully received. I'm pleased with the result but would be good to lose those halos!

God I love having an observatory in the garden!



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Yes, you're right. They are reflections caused by your Ha filters....very common in fact, particularly with astronomik filters before a certain date.

Apparently, astronomik will replace them if you send them an image.

I had the page on their site bookmarked but it doesn't seem to exist anymore unfortunately.

The reason they are offset is that something is not quite true to the focal plane.

I get exactly the same halos, and with my WO scope, they are offset due to focuser sag.



Edited by RobH

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Thanks Rob, I'll get in touch with Gerd then.

My WO also sags at the focusser, and (slightly) at the rotater for that matter. Not much but there's definitely play there. The focus barrel is very heavy as mine is the earlier 4" version. You can't eliminate it entirely or you'd lose the rotation. I thought it would be between the camera and the filter (wheel) where this angle must be?

Anyway, I'd like to eliminate this little problem so he is where I should start. I suppose if I can get the angle to be exactly 90 deg then I can remove using processing but it would be easier to not introduce them in the first place.

Cheers for now and thanks for the info.


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