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RE: Off-axis Parabolic Mirrors

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Posted by Robert May on July 15, 2000 22:30:40 UTC

The contrast is indeed a wee little bit higher than with the obstruction in there but the FOV is a bit smaller due to the coma that you get from the mirror. Remember that you are making a part of a larger mirror and thus, you get the coma of the larger diameter mirror with the light gathering and resolution of the smaller mirror. I haven`t bothered to sit down and see how undercorrected that you would want to make such a mirror because of this problem but I would suspect that not fully correcting the surface to the paraboloid would help with the coma problems.
If you want a clear aperture scope you may want to look into the Stevick Paul design which uses a normal parabolic mirror and two easy to make spherical mirrors. You can find the design on the web as one of the "weird telescopes".

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