Old 17-08-2013, 06:13 PM
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alocky (Andrew lockwood)
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alocky is offline
Join Date: Aug 2010
Location: perth australia
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CLS CCD filter star colours

There's been the odd bit of discussion about star colours when there's a CLS or similar light pollution filter in the train. I know Mario has had a few goes at restoring balance, and since the skies here have been so uncooperative for data acquisition, I thought I'd give the problem the benefit of my Great and Illuminating Mind and revisit some data taken using it.
My observations have been that whether using DSLR or OSC camera, or even LRGB filtering with a mono CCD in the backyard, you lose the gold- yellow stars.
To make yellow using RGB, you need some red, a little green and no blue. Given the throughput of LPR filters seems to be highest at the blue end, it seemed like the best way was to attenuate the blue channel in curves using a star mask to limit the adjustment to the stars only. This seems to work OK in the attached DSLR image of M31 from last year, except for the brightest stars which have been saturated in the blue. I guess the next trick will be to take some short subs that don't saturate and use them in HDR mode to fix the brightest stars.
Anyway - I thought I'd resurrect this discussion to see how others treat the problem.
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