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The Sun
Forum List | Follow Ups | Post Message | Back to Thread Topics | In Response To Posted by Walter Hamler on January 16, 2002 12:39:38 UTC |
Take a tape measure and hold it along the bottom edge of the mirror. Reflect the sun's image onto a flat surface ( I've found that a darker surface works best). Measure from the sharp image to the front, silvered, surface of the mirror. That is the focal length within at least 1/4 inch or less, depending how accurate you see the sharpest image and how steady you hold everything.
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