From: astroelectronic@t-online.de   
      
   > The pupil of the eye will be the limiting aperture if the system is   
   > designed for comfort, but it may or may not be in a test setup.   
      
   Let's assume that in a star test we use high magnification, so that the exit   
   pupil is smaller than the eye pupil. No vignetting.   
      
   > In the absence of vignetting, I think they'll be pretty similar since   
   > both are basically occurring in the pupil (of the telescope).  If the   
   > eyepiece were optically closer to the image, the effect would be less,   
   > because the phase errors would have mainly a local effect, and of course   
   > right at the image, it would hardly do anything except change the FOV.   
   > (It would be a field lens and not an eyepiece.)   
      
   That makes things complicated, because the Ethos eyepiece is a complex design   
   and at least one (field-)lens is in front of the image plane. As far as I   
   know, the optical layout hasn't yet been published. I tested the eyepiece as a   
   black box and I don't    
   know if the spherical aberration originates near the focal plane or near the   
   exit pupil.    
      
   Some pictures of the 21mm Ethos test setup:   
   https://www.facebook.com/astroelectronic/posts/428917360903364    
      
   Michael   
      
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