pov-ray/tuts/csgdemo.pov

  #version 3.7;
  #include "colors.inc"

  global_settings {
    assumed_gamma 1.8
  }

  camera {
    right x*1280/720
    location <0, 1, -10>
    look_at 0
    angle 36
  }

  light_source { <500, 500, -1000> White }

  plane { y, -1.5
    pigment { checker Green White }
  }


  #declare lens_hole = difference {
    intersection {
      sphere { <0, 0, 0>, 1
        translate -0.5*x
      }
      sphere { <0, 0, 0>, 1
        translate 0.5*x
      }
      rotate 90*y
    }
    cylinder { <0, 0, -1> <0, 0, 1>, .35
    }
  }


  #declare thing = merge {
    object { lens_hole translate <-.65, .65, 0> }
    object { lens_hole translate <.65, .65, 0> }
    object { lens_hole translate <-.65, -.65, 0> }
    object { lens_hole translate <.65, -.65, 0> }
    pigment { Red filter .4 }
  }

  #declare abox = difference {
    box { -1, 1 pigment { Red } }
    cylinder { -1.001*z, 1.001*z, 0.5 pigment { Green } }
  }


  intersection {
    object { thing }
    object { abox  }
    translate <0 ,.25, 0>
  }