From: "Jerry B. Hillman" 
To: 
Reply-To: "Jerry B. Hillman" 


Hi all,
I have discovered a problem with my Foucault test reading procedure.
Particularly in the outer zones the position of my eye becomes critical. A
little bit up, down, left, or right can alter the image drastically. I
believe this is because I am moving off center from the optical axis. My
last two sets of readings differed in the inner 5 zones by only .002",
but zone 6 varied by .01" and zone 7 and 8 varied by .015" and
.018" respectively..  I believe this explains, but not excuses, the
failure of my mirror to star test as well as it should have, and also
explains my failure to uncover the rolled edge during Foucault testing.  I
have tried the lateral wire test, and although it does give much better
visual differentialization between the outer zones, for me it is very
ambiguous in the inner zones.  It is also very hard with my tester due to
the extremely small later adjustments necessary for the KE.  The Everest
pin stick used with a KE suffers from the same ambiguosity in the center
zones. Is it feasable to test the inner zones with the standard Couder
masks and then switch to the Everest pinstick for the outer zones?

And now a really stupid question.  A which point do you decide that the
zone is nulled.
My method is to find the point that both sides start nulling equally and
continue to stay equal till the zone goes black. Is this proper, or is this
another error?
Clear skies, Jerry

--- BBBS/NT v4.01 Flag-4