Re: [ATM] how to use the foucault tester

["Jerry B. Hillman" <JBHillman@ev1.net>]

David,
I'm glad you decided to test the mirror before having it coated.

Go to this website.

http://www.atm-workshop.com/foucault.html

It is a 48 page document that describes Foucault testing in complete detail.
Download and print it out. You will not find a better description anywhere.
If you want to learn the Foucault testing method, read, and reread this
until you understand it.

As for your testing setup.  You will find that it is impossible to test a
mirror with the mirror leaning against the bottom riser of the stairway and
your tester on the floor at ROC.  You would be laying beside the tester to
get in the right position.  For a full series of tests, that is going to be
very uncomfortable.

First, build a test stand for the mirror.  It must be supported during
testing or it will fold over like a potato chip. Think in terms of the stand
supporting the mirror with the mirror leaning back and aimed at the tester
with the tester about waist high. You will have to find a way to deal with
the carpet so that the test stand is stable.  Then find a sturdy table of
some kind that you can put your tester on and elevate the back side of the
tester so that it is aligned with the mirror's focal axis.

Then it is a matter of practice to learn to use. If you have a web cam or
digital camera, take pictures of what you see.  You can post those and get
help from the list.  As they say, a picture is worth a thousand words.  That
saying really applies here since written descriptions are not nearly
accurate enough.

Clear skies, Jerry

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