From: rrllff@yahoo.com   
      
   Use the non sequential option in Zemax.  It's tricky to   
   master but you can model any shape.  It also allows you   
   to input from CAD.   
      
   Make sure that the angle cut of the Fresnel prisms is at   
   an angle that does not vignette the light.   
      
   However, if they are available, there are much better   
   tools to use than Zemax.   
      
   http://www.richardfisher.com   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)