[Author Prev][Author Next][Thread Prev][Thread Next][Author Index][Thread Index]

[ATM] Some questions on Tex versus Sixtests - Hoping I'm done!

Thanks to the group for all the hand holding lately - it's been a great help functionally and morally.  Jim, your guidance on working with Sixtests has added to my confidence in picking the next attack  each time.  Thanks to all others who have helped with this, too!!  Couldn't have done this without you all - at least not in less than 15 years.
 
By the Sixtests criteria, I believe I am done with this 8"  (Sixtest file at bottom of this post):  
 
Strehl = .990, RMS =   4.4nm,  s(RMS) = 1.0nm, 
P-V (surface) = 27nm  so wavefront P-V = 54/550 = 1/10 wave
 
However the Texereau analysis would indicate I am not done.  According to it, my wavefront error is about 1/3 lambda and zones 2 & 4 are throwing light at 1.6 times the Airy disk diameter.
 
The Tex approach does seem to give a worst-case scenario since it applies a single angular deviation across each entire zone, implying a very tight constraint on surface RMS in order to pass the test.  Is it fair to say that Tex generally overconstrains the criteria (especially the Airy disk constraint, since he's applying geometrical optics to a wave optics phenomenon)?   
 
 
Also, I thought the Rayleigh criterion considers two point sources resolved as distinct objects only when their diffaction spot centers are more than a whole Airy disk diameter (not radius) apart.  By that criterion, Tex's Airy disk radius constraint should really be an Airy disk diameter constraint.  Or is it that spot centers less than an Airy disk diameter apart (but greater than an Airy disk radius apart) are perceived as a single blurred image? 
 
Finally, in Sixtests is it advisable to put a value in for the obstruction diameter in order to get an idea of what the real-world performance of the mirror will be?  For an 8" f/6.4 mirror, is 50mm a good value to use (i.e., representative of a likely diagonal shadow)?  In the case of my mirror that would be great, significantly improves all performance parameters.
 
Thanks again!
Jay
 
 
File:
==================
51st Test Data Using Sixtests Analysis 1_30_05
202.4 0.0 Mirror, obstruction diameters (mm)
Foucault
0.0 Source distance (0=moving source)
y, mm X, mm
        18.263 1.8542
50.698 1.9545
74.790 2.5794
92.956 3.1801
*
0.000 2603.473 Conic targets:  b, R (mm)
0.1500 Measurement std deviation, mm
2597.9 Longitudinal reading bias, mm

======================================
 
 


		
---------------------------------
Do you Yahoo!?
 Yahoo! Search presents - Jib Jab's 'Second Term'
_______________________________________________
ATM mailing list http://www.atmlist.net/