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Re: Foucault Testing 8" F/4.5

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Posted by Robert May on February 7, 2000 18:19:23 UTC

The Ronchi test is not in agreement with the Foucault test! If the Foucault test is what you say it is, the Ronchi test will show a very sharp hook of the line edges on the edge area of the mirror. You aren't indicating this. Put about 4-5 lines on the mirror with the ronchi and you will see a hook right at the edge. If you don't see the hook then what you're doing is not right in the Foucault test. I might note that the extreme edge is difficult to really test properly because of the diffraction that happens on the edge that fools the eyes.

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