From: "Jerald F. Wright" 
To: "Sidor . Kurt" 
CC: atm{at}shore.net
Reply-To: "Jerald F. Wright" 


Kurt


I might point out that the Focault test done with a pinhole instead of a
slit might get you in the right direction quickly. I think that if you set
the knife so that the crest of the doughnut was in the center of the glass
that the crest would be an arc across the mirror centered on the parabolas
axis.  And its been suggested by Nils Olof that the lateral wire test would
be quite suited for testing an off axis segment of a parabola.  Done with a
pinhole either test I believe would show that arc. The lateral wire test
would probably do better and it would probably not have to be
"lateral" with a pinhole. On my tester for Ronchi testing I just
use a hair from my head attached to the knife movement and
sweep it laterally across the returning beam. With a pinhole it wouldn't
matter what the orientation of the "wire" was.

Jerry

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