Quote:
Originally Posted by Peter Ward
I suspect there are two things going on here:
the field is being vignetted (while you can "get away" with a 1.25"...a 36mm avoids this ) and....
You are getting a radial drop-off in filter performance due the converging light cone ) again a larger filter helps... a thinner filter set may also help here.
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Peter
I don't believe it is vignetting as there are stars/nebula in the corners that would be cut of if vignetting occurred. Also moving the filter closer to the rear of the corrector resulted in the circle getting larger instead of smaller as would be the case if vignetting occurred. As for “filter drop off” , analysis of the master flat (attached image) with the Ha filter placed in front of the corrector instead of between it and the camera shows a normal gradient expected from a newt. I beginning to think others have encountered this problem and said “yup it's vignetting” and either completely changed their configuration to eliminate the problem or blamed something camera/filter/corrector for their problem.
Cheers
Stephen