Re: [ATM] Ronchi testing

["Richard Ozer" <rozer@pacbell.net>]

You'll never see the lines exactly at ROC.  The test is designed to be used
slightly inside the ROC.  Print out your computer ronchi pattern (I assume
you have some software that does this) so that it's showing three lines on
each side of the mirror and then adjust your ronchi tester so that you see
the same number of lines in the same relative position as your print-out.
If the lines curve inward too much, then you are over-corrected; if they are
straight up and down, then you have a spherical surface, if they bow
outward, then you have an oblate surface.



----- Original Message ----- 
From: "Jerry B. Hillman" <JBHillman@ev1.net>
To: "The Amateur Telescope Makers List" <atm@atmlist.net>
Sent: Sunday, May 09, 2004 8:38 AM
Subject: [ATM] Ronchi testing


Hi all,
I have a stupid question but I am so frustrated I can't think straight.  I
have given up on Foucault testing for now.  The results I get vary so widely
that they don't make sense.
The ronchi test shows that at ROC I don't have as many lines as I should.  I
have to go inside of ROC to begin to get a matching pattern.  I should know
what this means but I need help.
Does this mean that I am hyperbolic? (lines curving too much?)  When I
adjust the conic value, I have to set it to about -.32 to get a matching
pattern at ROC.  This would seem to indicate that I am on the spherical
side,  But then working with negative values has always messed with my mind.
Is -1.0 more or less parabolic than -.32?
Sorry for the stupidity,
Clear skies, Jerry


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