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Old 07-10-2013, 04:47 PM
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pmrid (Peter)
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Reflections in Astronomik IIc filters

I am surprised by this but I am seeing pronounced reflections around the brigher stars in images using the Astronomik IIc LRGB filters. I had believed that the new series II had the problem licked. But I am getting it - mainly in green and less so in blue. It's a PITA.

Anyone else experienced this? The optical train in a Tak FSQ85 with a Tak .73 reducer into an ATIK 4000 - so not a huge chip. The scope is fairly fast at f3.9 (with reducer) and perhaps this is a contributor.

I'll attach a couple of examples and invite comments. These are both green filters.

Peter
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Old 07-10-2013, 08:24 PM
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Peter, I don't find this so much in the LRGB filters because I am using a system at f5.8, but I see this in the narrow band a bit. It is part of the reason that I shifted to Astrodon filters. I am not so alarmed by it though. It is just an aesthetic thing really. I see reflections like this in Mike Sidonio's images too in the LRGB shots, but I still don't think they look too bad.

I guess you have to decide whether you want to accept this optical thing or not.
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Old 07-10-2013, 08:34 PM
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Is it the same if you turn them around?

I have had several filters. The Astrodon Gen 11 seem the best for this.

Greg.
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Old 07-10-2013, 08:57 PM
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pmrid (Peter)
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Thanks Paul and Greg. I have an identical set of filters on my 10 inch F3.8 newt and am not getting these reflections. It looks like being a bit of a hunt to pin this down. If this heat gives me a break I'll do it this week but the outlook isn't great.
Peter
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Old 07-10-2013, 09:30 PM
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Hmmm that is odd. Perhaps like many things in sorting problems in Astronomy, it is a multitude of causes. I have had my Astonomiks filters replaced but still see this issue to some extent. It could well be that not only are the filter sets still producing some reflection issues but also the camera reflecting a little off the imaging window and also the reducer producing reflections. In other words I think it is worth if you really are bothered by the halos and reflections to look at all those areas. It could well be a combination of all three areas.
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Old 09-10-2013, 01:43 PM
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On some scopes the correctors can cause a reflection back and forth with the filter. I think this was the catalyst for the current 2nd generation anti reflection coated filters that the major players put out.

I use Astrodons on a variety of scopes but all either have a flattener or a corrector and I don't get virtually any halos in any colour. I did with Astrodon Gen 1 but not Gen 11. Baaders as I recall did give some in the green channel. I can't remember now if mine were gen 1 or latest gen.

Astrodon filters are the industry leader from what I have seen. Also Don Goldman is a nice guy. I got to chat with him at AAIC in the Gold Coast.

Greg.
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Old 09-10-2013, 02:10 PM
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I am using a reducer too but still get the reflections.

Yep spent quite a while talking to Don over the course of the AAIC. Was pretty mutual. I wanted to know more about filters and what would work for me and he wanted to know about planetary imaging. Really nice guy. enjoyed meeting him.
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Old 09-10-2013, 07:25 PM
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For some reason I think the fsq series seems to be more reflection prone...

Don't know why? Rear element?

Although I have not used astronomic filters I would share my own data.

I have an fsq106 no reducer, and stl11k. Originally I had custom scientific filters, but I dropped the blue one and it smashed, I didnt have haloes with cs filters. I replaced them with a astrodon gen 1 filters, and I got haloes galore. Replaced them with astrodon gen2 filters, No haloes.

Brett
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