RE: [ATM] Astigmatism need fixing? And how to do so?

["Jerry" <wa4guu@verizon.net>]

	How many sets did you take of each diameter?
	It may be a good idea to interlace your sets (d1 d2 d1 d2 d1 d2) so
that any temperature instability during the time it takes to test will more
likely average the same across both diameters.
	If you test diameter one several times and then diameter two several
times a change mirror temperature/equilibrium during the test cycle will
more likely appear as a difference between d1 and d2.
	The differences between your readings for d1 and d2 are not so far
out of line with what I would think an average person would be able to
repeat on testing one diameter testing only twice. The most difference is in
the center, which is the hardest zone to pin down.
	If you test carefully it takes time. Because it takes time there can
be a change in conditions from the start time until the finish time. The
glass can actually change shape from the first half of testing until the
second half.
	My opinion is that it is not likely that you have actually measured
astigmatism or measured something that is the result of astigmatism. I could
be wrong. I do think that under Foucault or Ronchi test you would see in the
center of your mirror something ugly enough to have caused you concern if
your differing readings were only resulting from astigmatism. Do you see any
thing like that or dog-biscuit. Dog-biscuit will cause some ambiguity in
zone readings. 

	I have probably said enough to get a thorough discussion boiling.
Oh... except to say if the astig is real and you are going to figure the
astig out I would suggest that you best go back to a sphere and do that
while concentrating on the things that one does to nullify forces that cause
astigmatism. Then parabolize while doing those things.

Jerry   
 
 
>>>>>>>

-----Original Message-----
From: atm J Killea
Subject: [ATM] Astigmatism need fixing? And how to do so?

Sheesh!  I thought I was done with this 8" f6.4, did some things to improve
on some TDE, got to some nice readings on the radius I have been testing all
along ("Axis 1" in the Sixtests files below) then I decided it was time to
check the perpendicular radius.  Not reassuring.  Yep, probably should have
checked sooner - out of sight, out of mind.
>>>>>>>>


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