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Old 12-05-2012, 10:49 PM
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Rigel003 (Graeme)
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unmounted filter orientation

I'm using the Baader 50.8mm unmounted LRGB set and by chance came across a reference on Cloudy Nights that they are direction specific. Apparently the newer ones have arrows on the edges showing which way they go, but otherwise you need to look at orientating the shinier side one way or you could have reflection problems (The documentation from Baader says towards the scope but many posters say towards the camera - not too helpful). Well I have been noticing some troublesome halos in my blue subs so thought I'd open up the filter wheel and check. In the end it was pretty much impossible to determine which side was the shinier one. I flipped the blue one to see if it will have any effect and took the opportunity to blacken the edges of all of them. Time will tell. Does anyone know a definite answer to this?
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Old 12-05-2012, 10:55 PM
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Shiny side def needs to face the light ie telescope to avoid reflections.

You can determine which side is shinier by have a bright light behind you. Angle the filter about 45 degrees to light on one side, then flip 45 degrees on same angle the other side. One side will definitely have more of a metallic shine to it. This is the side that faces the light. Most of the baader filters have a v scored into side. It can be hard to see. The pointy end of the v few the telescope. The wide end the ccd chip.
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Old 13-05-2012, 01:15 AM
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Merlin66 (Ken)
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Definately "shiny" side towards the sky.....
(if you link the guys who advocated otherwise I'd be more than pleased to correct them!!!)
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Old 13-05-2012, 01:56 AM
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Rigel003 (Graeme)
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This is one of the threads.
http://www.cloudynights.com/ubbthrea...l/fpart/1/vc/1
The last few comments are talking about facing the camera but I can understand that reflecting light away from the camera makes sense.

With my filters I can't clearly see a shiny and non-shiny side, but I can see the "hall of mirrors" effect on one side that someone mentions. Maybe this is the anti-reflective side and should face the camera as described. All this may be easier in bright daylight.
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Old 13-05-2012, 03:54 AM
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pmrid (Peter)
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Quote:
Originally Posted by Rigel003 View Post
This is one of the threads.
http://www.cloudynights.com/ubbthrea...l/fpart/1/vc/1
The last few comments are talking about facing the camera but I can understand that reflecting light away from the camera makes sense.

With my filters I can't clearly see a shiny and non-shiny side, but I can see the "hall of mirrors" effect on one side that someone mentions. Maybe this is the anti-reflective side and should face the camera as described. All this may be easier in bright daylight.
I'm interested in this too since I have some Gen 1 Astrodon filters to mount. Here is a cut from the FAQ on the Astrodon site:
"Orientation does not matter, Gen 1 filters had a "^" marked on the edge. Gen 2 LRGB, photometric filters and narrowband filters do not. This is a recognition that orientation does not matter in terms of spectral performance. It is widely believed that facing the shinier side of the filter toward the incoming light, i.e. the telescope, somehow eliminates or minimizes reflections between the highly reflective CCD and the filter, but no evidence has been provided. That would be akin saying that there is a significant reflection difference between a first surface (reflective coating on the front surface) and second surface (cotaing on the back side) mirror. Although there may be minor differences, if you have an optical problem with one, you'll likely have an optical problem with the other. In imaging, it is a system property of your scope, f/ratio, location of the filters in the light path, how far off axis the light is and the distance to the detector, etc. So, until data are put forth that demonstrate an effect, we will continue to advocate that orientation does not matter. However, for the sake of consistency during troubleshooting, you may consider mounting all filter one way or the other regarding the most reflective side."
http://www.astrodon.com/articles_faq...ase:391,355,51

Peter
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