[ATM] diagonal flat testing

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

Hi All,
At the suggestion of Ken Hunter, I set up my Foucault Tester with the
spherical 5" primary from my Meade scope.  After getting everything aligned
I did the Foucault null test for a sphere and also a Ronchi test.  As
expected, both tests showed a decent spherical surface.
Then I added the diagonal flat into the light path about 12" away from the
light source.  Of course this required turning the tester at right angles to
the mirror, and angling tester and both mirrors to get everything back into
alignment so I could see the reflected light.  Now the light is passing
across the diagonal flat twice.  Once on the way to the mirror and again on
the return path.This wasn't an easy task to get set up.
Results however seem to confirm that the diagonal flat is indeed polished
flat.  At least I still get the same results when doing the null test and
the Ronchi test.  I would assume that if the diagonal was not correct I
would be able to detect problems in one of these tests.  Incomplete nulling
of the sphere or crooked or twisted Ronchi lines.  By the way, the Ronchi
lines were straight, edge to edge, both sides of focus with as many or as
few lines as I cared to display.
I would like to be told if my testing method was invalid or incorrectly
done, as I have never attempted this type of test before and I intend to get
this flat and the 16.5" coated next week provided that the 16.5" passes the
set of Foucault tests I am about to run on it.
I'll check my e-mail again before I send these mirrors off Saturday just in
case.
Clear skies, Jerry


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