From: dave.scienceman@gmail.com   
      
   Hi,   
      
   I just found this forum, and it seemed like the perfect place to ask about   
   this.  I have an older Shack-Harmann WFS from WaveFront Sciences.  I was using   
   it to check colimation for a holography set-up, and no matter what, the   
   minimum measured astigmatism    
   was ~lambda/10.  All other aberations (defocus, coma, spherical) were   
   ~lambda/50.  THe RMS wavefront deviation is ~lambda/30, mostly due to   
   astigmatism, it would seem.     
      
   After some digging, I found a Blue Sky Collimeter in the back of a cabinet in   
   the lab, and used this for an independent measure.  The beam *blinks* on and   
   off - so it would seem the phase is very flat.   
      
   I tested the calibration of the WFS by placing it several meters from a   
   pinhole, and measuring the radius of curvature.  It was within the error of my   
   tape measure.   
      
   Is there a minimum phase error a WFS, or its software, can measure correctly?    
   As in, if the error is too small, numerical noise or something else becomes an   
   issue?  Could it be that after all these years, the hardware no longer matches   
   the calibration    
   file?   
      
   Thanks for any feedback,   
   David   
      
   --    
   David Miller   
   Graduate Research Assistant   
   Department of Electrical Engineering   
   University of Colorado   
      
   --- SoupGate-Win32 v1.05   
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