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Old 12-04-2011, 04:30 PM
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peeb61 (Paul)
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reflection error

Hi All,
I'm having a problem with bright stars and a reflection error.
The attached image is over brightened to show what I mean and is a crop of the area around NGC4945.

The reflection looks like a reflection of primary and spider.

The imaging train is as follows....Orion Deep Sky Filter>Nose Piece>Canon T-Adaptor>Coma Corrector>Camera.

Any help in resolving this would be great.

Paul
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Last edited by peeb61; 12-04-2011 at 05:00 PM. Reason: More details
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Old 12-04-2011, 04:36 PM
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Merlin66 (Ken)
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It's a reflection from you filter showing on the image.
Either change the filter to a better one (Astrodon etc) which has less reflections or leave it out of the image train.
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Old 13-04-2011, 07:51 AM
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peeb61 (Paul)
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Thanks Merlin66,
I was kinda' hoping it wasn't that but I had my suspicions. The light pollution in my location is reasonably bad so there is a strong need for a filter. I will expose without this filter and see how that goes and I will try and borrow from one from a club member and see if that resolves it.

I will post back at some stage with the results.

Paul
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Old 13-04-2011, 08:30 AM
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multiweb (Marc)
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Hi Paul, this looks very familiar. Looking at your imaging train I can tell you exactly what it is because I've been plagued with these for years. It's a reflection between the glass of your camera nosepiece and the back of your MPCC. The only way to minimise this is to get rid of the glass on the camera nosepiece so you increase the distance between the MPCC and the next reflecting surface which should be your camera CCD.
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Old 13-04-2011, 09:06 AM
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peeb61 (Paul)
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Thanks Mark,
Very interesting! So if I got rid of the DSF and refocused this would eliminate this reflection? If I got one of the Astronomik EOS clip in filters for light pollution I might be able to get away with it?

Or will it be a test and tell?

Paul
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Old 13-04-2011, 10:46 AM
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multiweb (Marc)
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Quote:
Originally Posted by peeb61 View Post
Thanks Mark,
Very interesting! So if I got rid of the DSF and refocused this would eliminate this reflection? If I got one of the Astronomik EOS clip in filters for light pollution I might be able to get away with it?

Or will it be a test and tell?

Paul
In my case getting rid of all the glass layers between the MPCC and the CCD helped. I've never tried inserting a filter between the two though. My filters have always been after MPCC at the end of the imaging train. You might try it. But I'd suspect any filter with a mirror like surface such as Ha for example would make things worse as it would reflect the back of the MPCC onto itself.
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Old 13-04-2011, 11:41 AM
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peeb61 (Paul)
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Thanks again Marc,
Food for thought. I might try and image a couple of subs without the DSF and see how long I can image before the image becomes washed out with the light pollution...I never know I might surprise myself.

Paul
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