Telescope-Accessories-Optolong H-Alpha 7nm CCD 31mm Unmounted Filter

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1. Al E. Verified Buyer – 1 September 2018

   The 31mm Optolong 7nm 31mm diameter filter is all glass. There is no plastic or metal rim surrounding the edge, just a thin layer of black paint. Thus, the greater diameter does not vignette the corners as much as filters with screw in cells. On my QSI-583 camera the extreme corners with the Optolong Ha filter measure 89% transmission. My Orion fi

   lters average just 74% transmission.
   I had two problems:
   1. The filter is very thin. This required rubber spacers (not provided) to be inserted in the filter port to raise the filter slightly above the filter wheel so the locking screws and nylon washers can hold it in place.
   2. Interference filters are normally inserted so the highly reflective surface it toward the sky. However, with this arrangement created a reflection of the sensor during imaging. I reversed the filter and the problem disappeared.
   So far I have taken only one test image with the filter. That was through haze with light pollution and moon glow creating an SQM of 18.4. The North American was clearly apparent in 5 and 10 minute subs at F5.4.
   In conclusion, the Optolong 31mm Ha filter seems to be a good purchase. Port spacers, retaining screws, and a sentence or two of instructions would have made the installation considerably less time consuming.