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RE: Cassegrain Primary Imperfections....

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Posted by Bill on September 4, 2000 11:20:04 UTC

If the "swirls" affect the quality of star images then they are bad.

Get Suiter`s star testing book, which is available here:

http://www.willbell.com/tm/tm5.htm

The book covers mirror surface roughness and what to look for in star images.

If possible, test the mirror with a foucault or ronchi tester. They can be very helpful in determining if the mirror has a rough surface or other defects.

Hopefully, the coating is to blame and there are no serious imperfections ground/polished into the mirror. Recoating an 8" is not too expensive.

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