Re: [ATM] Weird Foucault readings

["Jerry B. Hillman" <JBHillman@ev1.net>]

Hi Bob and All,
I set my Foucault tester up the same way it was last year.  Big piece of
wood in my living room. Mirror at one end on the floor, tester at the other
end about eye level.
I then started running tests.  After running three sets of readings I
determined that the readings are consistant.  And match the readings I took
Friday evening.  Those are the readings I posted to the list. I don't know
if they are correct. I just know that the readings only vary by about .005".
Perhaps if I take 100 sets of readings that do not vary by more than .005" I
can begin to believe that I have learned how to do the Foucault test and can
begin again to figure this mirror.
The one thing I am doing different that I have not done before is I have
masked the opening that I look through down to 3/64"  The left side of the
mask opening is just behind the KE.  I can just see the mirror plus about 2"
outside when I look through it.  It forces me to be consistant with my eye
position.  To far to the left and the left mask opening goes behind the KE.
To far to the right and the right mask opening goes suddenly black.
I don't know how many sets of readings I should take before I can be sure
that I can begin to correct the figure.  The only thing I know for sure is
that I wasted the last 6 months.  The mirror is on the parabolic side of a
sphere, but definitely not finished if these readings are accurate.  Since I
totally missed the Mars approach I don't need to have a deadline to finish
this mirror.  Money is kinda tight to so it has to be right the first time I
get it coated.
I'll keep the list posted.
Clear skies, Jerry
(I got 4.4" rain today so clear skies are a wish.)


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