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Old 13-05-2012, 03:54 AM
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pmrid (Peter)
Ageing badly.

pmrid is offline
Join Date: May 2008
Location: SE Qld
Posts: 3,090
Originally Posted by Rigel003 View Post
This is one of the threads.
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.",355,51

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