d00a5647   
   From: rrllff@yahoo.com   
      
   On Dec 10, 8:04 am, Jeff  wrote:   
   > Dear Samlon and Anorton,   
   > Thanks for your kindly reply!   
   >   
   > Here I am in a inspection room of an OEM and have not many options and   
   accessories, even a retro sphere.   
   >   
   > I understand Anorton's suggestion that weak refractive index gap contribute   
   less on final wavefront. But as OEM, measuring is the top priority. I will try   
   Anorton's configuration on flat mirror, which should bring less astigmatism   
   than my own.   
   >   
   > The thinking to decrease aperture of measuring beam comes from below points.   
   1, The small aperture bring much less Spherica aberration, which may bring   
   much less overlapping effect. 2, The IRR happens in central area.   
   >   
   > The IRR fringe is so like a discontinuous function. I just can not imagine   
   it caused by polishing process. Maybe it comes from uneven UV curing.   
      
   If you want sensible replies do not use abbreviations.  What is IRR?   
      
   However, discontinuity in fringes can be caused by polarization   
   problems.  If you have folds in your optical system which are not at   
   90 degrees then you will see such discontinuities.  They can be   
   cleaned up if it is possible to place a linear polarizer somewhere in   
   you system.   
      
   As Adam pointed out (more or less) it is extremely unlikely that a   
   cemented surface is resulting in wavefront errors.   
      
   http://www.richardfisher.com   
      
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