From: etaloncn@gmail.com   
      
   Hello everyone,   
   I have some mid-sized cemented doublets, diameter about 40mm. From fringes   
   after cementing curing, I can see some bad irregularity of surface form. I   
   want to ensure this irregularity without splitting doublets. I already failed   
   in two ways.   
   1, Focus Zygo beam at spherical center of cemented surface (already   
   transformed by the first surface)   
   2, Put plan mirror at focus point at transmitted beam though doublets. Check   
   the reflected wavefront. For the irregularity is not like astigmatism. So, I   
   think plan mirror does not interfere trouble shoot too much.   
      
   But above methods does not work either, for the interferogram seems to show   
   some overlapping effect and it does not match what is seen directly on fringes   
   in cemented surface. I think maybe the first surface bring some spherical   
   aberration to wavefront    
   or rest sperical aberation of doublet take some effects. Now I am thinking   
   whether decreasing aperture helps or not.   
      
   Does anyone have advices on it?   
      
   Thank you very much!   
      
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