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Posted by Robert May on December 20, 2001 21:45:58 UTC

Go look up the Stevick-Paul design.
The offaxis parabola produces coma if care isn't taken to remove it from the end product. It's the nature of the beastie. Long focal length newtonian designs help by making the coma very minimal even when a offaxis spherical mirror is used.
Short FL designs make a lot more problems than long FL ones do. Unfortunately, long FL designs also don't have the FOV of a short FL design so it's all a tradeoff.

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