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Posted by Steve Campbell on February 24, 2002 12:29:05 UTC

Your calculations are correct,you should have a 0.055 depth for an 8"/f9, however 1/16" is 0.0625
so FL=radius squared/4(d)....=64" divided by 8 = 8, F/8 is your focal ratio,you overshot,16/4x0.0625=64",use reflected sunlight to confirm this,wet the mirror with soapy h20,
you may be happy with f/8, if not, grind with tool on top to increase FL,check FL FREQUENTLY,but use reflected sunlight to check this, feeler gauges and drill bits are not a very accurate means of measuring FL, dont use too much "over-hang" if you must increase the FL!,the natural tendency is to do so, you'll roll down the edge if you do!
Good luck.

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