Quote:
Originally Posted by ASTROMONK
Hello Ivo..
Thanks for reply....the background is a constant, even colour tint, usually mauve. I am familiar with light pollution and use a TLS (Astronomik) filter when this is a problem. M51 looks orange with or without the filter!
I took images of the Orion region with a Tak. Epsilon These were fine. I tried M51 with the 10" RC and came across this problem. The RC is much slower, f8 as opposed to f3.3 for the Epsilon. So the signal to noise is worse. It could be just that, as I am trying to extract signal from the noise floor??
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Getting rid of an even bias during image processing shouldn't be too hard - just use a pedestal in the red and blue color channels using a curve manipulation tool of your choice.
It'd be better to eliminate the cause of it during acquisition though.
Of course, a scope itself should not induce any type of bias, so the culprit has to be elsewhere. Normally I can think of a few causes but these don't explain the different results you're getting with 2 different mirror based scopes. The only difference I can see is the Tak having a built-in field corrector lens (if I'm not mistaken?), which may interfere with how any (present or absent) IR/UV cut filter would influence the image. A slight magenta cast is consistent with an absent IR filter.
To be honest though, I can't see anything wrong with the image you attached - background levels are perfectly fine when I inspect their RGB values?