From: "Marco Miglionico" 
To: "ATM Archives" 
Reply-To: "Marco Miglionico" 


A have a question about optical testing which will expose my ignorance of
mirror making. Is the Foucault test the test used when measuring the
accuracy of a mirror ie 1/th wave etc..?

Does anyone do this test or other tests while the mirror is in the support
cell that is going to be used in the scope. (Mirror pointing straight up).
The reason I am asking is that there are often complaints that the sag in
thin mirrors while using the Foucault apparatus (mirror on its side) is
objectionable. Could two birds be killed with one stone if the mirror was
tested vertically in it's proposed mirror cell. The cell would of course
have to be much better than needed ie enough supporting points such that
the deformation of the mirror surface (and resulting wave front) was of a
magnitude greater than that needed, so that it is the mirror one is
measuring and not the supportiveness of the cell.

Could one, in practise, measure the wavefront effects of various support
cells on the mirror using Foucault (or other) aparatus?

The accuracy of PLOP seems to be taken for granted so could this PLOPical
theory be backed up by directly measuring the same mirror using the same
cell computed in PLOP? That way a direct comparison could be made between
the model mirror surface in PLOP and the actual mirror deformation measured
in optical tests with the cell.

Sorry rambling .........again..

Marco.

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