[ATM] Foucault multi diameter and Interferometry profile comparison

[Dale Eason <atmpob@yahoo.com>]

I have stumbled only somewhat of a puzzle.

I have been comparing the surface profiles of mirrors
tested with my Robo and interferometer.  What I have
found is that they agree very closely when using only
the symmetric Zernike terms.  That is only the
spherical aberration terms are used to match the
surface.  I think that is what Roger Ceragioli's
software does to create the average p-v profile shown
in the round robin results.

The average is independent of the rotation of the
mirror, that is diameter 1 and diameter 2 will be the
same.  In fact that is what my robo data for mirror C
shows.

I was thinking that Foucault only measured the
spherical aberrations and my testing with mirror C
(the one with the most Astig) bears that out.  However
the general technique of Foucault testing is to test
across two different diameters.  From the above
statements and experiments this does not seem like
necessary step.

When we do get different readings by rotating the
mirror, I think we might really be measuring how the
test stand and gravity deforms the mirror at different
rotations.

Can any of you think of other explainations.  For
instance perhaps Foucault can see some of the other
aberrations.  But if that was the case then it should
show up the the profiles created from Foucault data
but it does not.

Dale Eason




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