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

[J Killea <jkillea@yahoo.com>]

Jerry, thanks for the thoughts...
Yes, I actually took 4 sets of each diameter, and I also took 4 sets of each last night, too. 
 
Based on certain measures, I'm feeling better about the mirror:
 
Both days same basic result, although my surface RMS errors were 2.6nm +/- 0.6, and 8.7nm +/- 1.9  for each axis respectively yesterday, and today they were 5.7 +/-1.3,  and 13.3 +/- 2.9.  So by one way of figuring (grateful to Jim Burrows for this) yesterday's tests easily pass the 1/28 wave test based on RMS and today's pass with a little wiggle room.  (By the way, I took the combined RMS of the 2 axes and added in twice the sigma(RMS) from Sixtests): 
 
Combined RMS + 2*sigma RMS 
  = sqrt( [(RMS axis 1)^2 + (RMS axis 2) ^2] / 2)  + 2*sqrt ( [s(RMS1)^2 + s(RMS2)^2] /2)
 
That result needs to be less than 1/28 wave, about 20nm, and in both cases it is.
 
 
Nope, I did not interlace the diameter measurements as you suggest, although the thought crossed my mind.  The mirror had not been worked on prior to today's measurements, although I did give it a quick dunk in the room temp water bucket before putting it on the test stand.  
 
Don't really have any dog biscuit, and it does look like the worst measurement differences are in the single central zone, which is reassuring.  
 
So, I am convincing myself to leave things be, but I also have a gnawing desire just to take one shot at bettering this - scary!  As I implied in my original post, a star test would be ideal right about now...  just need a scope to test with.  Will see if I can find someone in the San Mateo Astronomical Society.  Oh yeah, and I also need someone to walk me through the star test!
 
Jay



		
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