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Old 23-02-2012, 10:35 PM
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Whats causing this Halo ?

Anyone got ideas what might be causing a Halo around a bright star on Green and Blue Filters ?

I took some 10 min exposures tonight gathering color data and I noticed my Green and Blue filter exposures had a bright halo around one of the saturated stars.

I have attached a picture.

The red filter does not have this. They are parfocal Astrodon Gen 1 filters.
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  #2  
Old 23-02-2012, 11:29 PM
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What setup are you using. Does this happen without a filter or a clear filter?
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Old 23-02-2012, 11:50 PM
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Setup is ST-2000xm with CFW8A on a Tak FSQ106

There is no halo in red filter. I have not tried a clear for this long on this system yet.
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Old 24-02-2012, 01:04 AM
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I have no experience with this setup, but, are the filters clean or the window on the camera clean?

What does this calculator show you?
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Old 24-02-2012, 10:22 AM
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Reflections off the filters. Gen 11 have anti reflection coatings as most scopes these days have correctors and especially with the larger chips reflections became a real issue.

I used to get reflections like that sometimes with green. Occassionally with blue. These are mirrored type filters. Also do you have them facing the right way? Mirrored side towards scope?

Greg.
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Old 24-02-2012, 11:37 AM
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Thanks Greg. Never knew there was a right way around. Will double check the installation of the filters.


Quote:
Originally Posted by gregbradley View Post
Reflections off the filters. Gen 11 have anti reflection coatings as most scopes these days have correctors and especially with the larger chips reflections became a real issue.

I used to get reflections like that sometimes with green. Occassionally with blue. These are mirrored type filters. Also do you have them facing the right way? Mirrored side towards scope?

Greg.
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Old 24-02-2012, 11:49 AM
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Hello Chris, many interference filters show similar hallmarks, and while AR coatings help, reflections can still pop up from deeper down in the filter.
( FYI some narrow band filters have 64+ layers)

They are also spectrally localized....and can get worse at the peak QE wavelength of your camera.

There is usually no easy fix, other than to try another filter or manufacturer. Making sure your filters are exceptionally clean also helps.
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