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Vignetting Reported By Newt V2.5

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Posted by Dave Sellors on February 19, 2003 18:03:45 UTC

Hello all:

I'm new to telescopes. Got Richard Berry's telescope making book for xmas, have my heart set on a 10" dob. I've used Newt to optimize the design, but I need to understand something before buying any parts.

What controls the width of the white line (the point of focus) above the focuser ? It seems this is significant to vignetting. My design using a 1.25" focuser is marginal. I call for a 1.8" diagonal, but Canadian sources offer 1.83." Just increasing the diagonal size by 0.03" introduces a vignetting problem.

Changing to a 2" focuser rids the problem, but my budget won't support 2" eyepieces. If I go with a 2" focuser with a 1.25" adapter, I think I will get vignetting problems again, but Newt can't analyze this situation directly.

I'm tempted to stick with my present (marginal) design, but I need experienced advice here. Any suggestions ? I would gladly forward my Newt specs if someone has the time to review them.

Thanks.

Dave

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