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RE: Measuring Focal Length

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Posted by Rick Crockett on May 27, 2000 05:30:43 UTC

Build a small open faced box for the mirror to sit in. Attach a 2x2 post to the side sticking up from the open box. Make a cardboard slide that can be moved up and down the post and extends past the center of the mirror. Put the mirror in the box, point it toward the moon and move the slide until the moon is in focus. Tape the slide in place and measure the distance from slide to mirror.

You can also use the foucault test and divide the mirror to knife and pin-hole distance in half.

God Luck,

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