To: atm{at}shore.net
From: mdholm{at}telerama.com
Reply-To: mdholm{at}telerama.com


Recently I had fairly good results using the Foucault test with very narrow
maks openings near the mirror edge to help map a turned edge and the
various peculiar shapes I got it into while trying to reduce it.  The
narrow zones were not easy to read, and I was uncertain at first whether to
believe the results, but after I saw that the results seemed to be
reasonably consistant, and seemed to show the changes that should be
expected from specific figuring tricks, I gained more confidence.

I used mask openings 1/2 the width of the usual edge zone opening, and
spaced them just a few millimeters apart near the edge.  It takes more than
one mask, because you want to get the readings from the "normal"
zones at the same time in order to be able to put the edge readings into
perspective.

I ended up with 10 zones on an 8 inch mirror using three masks.  Yes it was
a pain to measure all those zones, but the confidence I gained that I was
acutally seeing what was happening on the mirror made it worthwhile.  BTW,
I use Sixtests to reduce the data.  It works great.

Mark Holm
mdholm{at}telerama.com

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