When rendering one of the test-scenes with (Version 3.6.1 (g++ 3.4.1 @
i686-pc-linux-gnu) there is an obviously non-realistic behaviour:
Light, transmitted by a glass of given refraction, does not behave correctly
when projected onto a plane behind the sphere. The refracted light gives
ever the same pattern, independently of the given "ior".

I posted this to the bug-report-site, but the last previous post there is
from 2006, so here again: for the effect to be seen, either use the
following two files and run them yourself, or just download them from
    http://manganese-blue.com/index.php?main_page=page_3,
where you also can examine the readily-rendered images.

> following 2 files to be saved into files and run on any standard linux

----------------------------------save as eg. "driving.pl"------------------
--------then chmod 755, then run, but save file below first----------------
--------nothing magic happens: just put values for "ior" into the scenefile-
--------and post-processing of the generated images----------------
#!/usr/bin/perl
$=$/;
system "mkdir anim";
system "rm anim/*";
for($i=1;$i<=1.9;$i+=0.1){
        print $i;
        system "cat reftest.pov | sed 's/xiorx/$i/g' > actual.pov";
        system "povray +Q9 actual.pov";
        $istr='"'.'index of refraction (ior): '.$i.'"';
        system "convert actual.png -fill white -draw 'text 10,10 $istr'
actual$i.png";
        system "mv actual$i.png anim/";
}
--------------------------------------------------------------------------

------------scene-file (name it "reftest.pov", so that the above script---
--------------can find and manipulate/execute it several times -----------
global_settings {
  assumed_gamma 2.2
  max_trace_level 25
}

#include "colors.inc"
#include "shapes.inc"
#include "textures.inc"
#include "glass.inc"
#include "stones.inc"

camera {
   location  <0.75, 3.5, -3.5>
   direction <0.0,  0.0,  0.5>       //  "wide-angle" view
   up        <0.0,  1.0,  0>
   right     <4/3,  0.0,  0>
   look_at   <0,    0,   -1>}

// Light sources, two to the front, right, on from the left, rear.
//light_source {<-30, 11,  20> color White}
//light_source {< 31, 12, -20> color White}
light_source {< 32, 11, -20> color LightGray}
light_source {< 32, 11, -20> color LightGray}
light_source {< 32, 11, -20> color LightGray}
light_source {< 32, 11, -20> color LightGray}
light_source {< 32, 11, -20> color LightGray}

union {
   // A green glass ball inside of a box-shaped frame
   sphere { <0, 0, 0>, 1.75
      interior{
         caustics 1.0
         ior xiorx
      }
      texture {
      //   T_Glass1
      Glass2
//      White_Marble
        pigment {color green 0.90 filter 0.85}
         finish {
            phong 1 phong_size 300         // Very tight highlights
            reflection 0.15                // Needs a little reflection
added
           // reflection xiorx                // Needs a little reflection
added
         }
      }
   }

 plane { y, -1.5
   texture {
 //      T_Stone1
        White_Marble
      pigment {
         octaves 3
         rotate 90*z
      }
      finish { reflection 0.10 }
   }
}
--------------------------------------------------------------------------

Upon examination of the generated pics it's clear that the focal-length of
the sphere-lens does not vary as it should with the ior.

Again: see http://manganese-blue.com/index.php?main_page=page_3
for the ready stuff.

More bugs to follow ...

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