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RE: Help,ceramic Tiles Focal Length

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Posted by Rick Crockett on August 3, 2000 18:24:12 UTC


You can use drill bits to determin the depth of curve know as Saggita. Shimms would be better. Do not use bits once into polishing because it is too easy to scratch the surface.

My version of the formula is this:

Fl=D^2/16S or S= D^2/16Fl

In your case:

D=8", Fl=40" so S=8"*8"/16*40"=64""/640"=1/10th inch or 0.100" for Saggita.

I have a wooden box that I an set the primary in and near one corner it has a 2x2" pole with a sliding cross arm made of cardboard. If neccessary I soap up the mirror (in the rough grinding stage) and reflect an image of the sun onto the cardboard. Measuring the distance from mirror to focus gives me the focal length. When you have a good polish the Foucault method will give you an extremly accurate measurement for Radius of Curvature which is just twice the focal lenght.

Have Fun,

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