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Foucault Testing 8" F/4.5

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Posted by Jim S./">Jim S. on February 3, 2000 18:31:03 UTC

I'm testing my first mirror (8 in. f/4.5) and can't get the edge to shadow test. The right edge goes into the heavy shadow but the left side stays lit (Knife enters from the right) Do I need to re-adjust the lateral as I test the outer zones or leave it alone? A Ronchi test looks picture book from inside to outside and the surface looks smooth. I'm also having a problem with the edges of the silt showing up in the mirror during testing. If I widen the slit the problem goes away but then what's the fuss about narrow slits and tint pinholes in Texereau. Out to the 70% zone things are as expected.

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