Re: [ATM] Lens Wedge

[Anthony Stillman <atmer@flash.net>]

James,
   
  I too looked through a bunch of books and only found cautions and stringent criteria for achromatic lens wedge.  No qualitative equations.
   
  So I plugged a few frounhofer designs into OLSO and started tilting surfaces.  Qualitatively I've learned that a little wedge is no big deal.  This is particularly so of the crown element.  The effect was about five times worse for the flint element.
   
  In both the 150mm f/15 and the 125mm f/18 design (BK7, F4) , one third of a degree of wedge seems to be the pardonable limit for the crown element.  This amounts to about 3/4 of a millimeter.  One half a degree is clearly too much.  The MTF shows that, as one would expect, the mid and high spatial frequencies are what suffer.  Astigmatism is the principle cause, not chromatic abberation.  Of course chromatic abberation in a doublet is pretty awful anyway.  A slightly prismatic lens doesn't seem to make it much worse.
   
  Lastly, in the last few years I've made a half dozen lens (four of them singlets) and holding wedge to a few mill was easy.  Getting it under 0.001 inches and holding CT was tricky but it was easier than figuring.
   
   
  Anthony
   
  plurimi in pace vivere volunt
  Most men want to live in peace.
   
   
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