ATM Foucault test questions

["Bennett, Thomas D" <thomas.d.bennett@lmco.com>]

Hi everyone,

Just tried using a Foucault tester for the first time using a finished
commercial mirror (10" F5.6) as a test optic and have a few questions:

        I think I see the parabolic image shape but it appears very subtle
(very low contrast). The only quantitative conclusion that I could make is
that there dosen't appear to be any zones on the mirror. Is there some way
to make the image more obvious? I'm not sure I can do any quantitative
testing unless there is a way to make the image more apparent. Since the
test mirror is aluminzed; would an un-aluminzed primary produce a more
obvious or less obvious image? Does one get significantly better at
seeing/testing mirrors with the Foucault test the more it is done?

        Would a home-made interferometer (as described in recent ATM
postings) produce a more apparent image for mirror testing?

                        Thanks - Tom