Quite often I read on internet forums doing narrowband astrophotography with a one shot color (OSC) cam was nonsense. I never understood why that should be the case. Of course 3/4 of the RGGB pixels remain un-used. But nevertheless it should work.
Two days ago I took a shot at it and attached a Baader 7nm h-alpha filter to my ASI 294Pro cam. In downtown Frankfurt, a heavily light polluted area, I took 12x300s test photos of NGC 7000. This is the "raw" result, just stacked and stretched.
All green and blue pixels are still present. They add nothing but noise to the picture. Once you extract the red channel thus get rid of the green and blue noise, the result is monochrome and looks like this:
I used a TS107-S with TS Flat 2,5 (107/700) on a Losmandy G-11.
That is superb, and proof that it can be done.....and very well to..
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