From: "Herb Kasler" 
To: "Jerry B. Hillman" , 
Reply-To: "Herb Kasler" 


Jerry,


RE:

> So it didn't work.  The pitch lap mold is great for 12" and smaller but is
hard for larger mirrors.  <

Who cares? I think you should forget about making a new tool. Whatever you
did the last few sessions worked! Now it is really time for you to stop
flogging the glass and start taking some readings on that mirror. I don't
think you're actually finished, but you're close enough to start looking at
numbers. Make yourself a nice, accurate pinstick (forget about the Couder
mask-it's not what you want for your type of mirror). I would reccomend no
less than 11 zones for a mirror that size. Try to get as close to the edge
as you can. Make a wire bow out of a paperclip and stretch a human hair on
it that you've painted black with a Sharpie. Use that instead of a knife
edge in your Focault rig (with a slit or a pinhole light source). The wire
test is much more accurate for a mirror as big and short as the one you're
making. When you try it, you'll see. Then (if you haven't already) download
Sixtests from Jim Burrows. It is a positively excellent program for
interpreting Focault numbers, and more importantly, for planning your next
figuring step.

Then spend a day getting some nice, accurate numbers on your piece of
glass. You may find that you're in the home stretch.

Good luck,

Herb.

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