Don Barron wrote:
> 
> Does anyone have any suggestions as to how one might simulate the vignetting
> in early camera lenses. So for example how to control the brightness of the
> image in terms of its angular distance from the look_at according to cos(
> theta)

Not angular brightness, exactly, but if I understand the artistic
effect you're shooting for, try this instead:

Sample may need adaptation for your particular scene, but it will 
do to decide if it's what you need. Animation of scale could
be made into a wipe effect, the color of the border is variable
at need, and different patterns will allow for different border
shapes...
-----------------------------------------------------------------
#include "transforms.inc" //needed for Reorient_Trans

/*camera location and look_at are declared because the effect
  depends on them later... */
#declare CamPos=<0,10,-20>;
#declare CamTarget=<0,2,0>;
#declare CamAxisDiff=CamTarget-CamPos;

camera {
    location CamPos
    look_at CamTarget
}

plane { //this is the filter...
    y, -0.9*vlength(CamPos)
    pigment { 
        wood
        color_map {
        [ 0 rgbt<0,0,0,1>  ] 
        [ .25 rgbt<0,0,0,1> ] 
        [ 1 rgbt<0,0,0,0>  ]
        }
        rotate<90,0,0>
        scale 2.25        
   }
   no_shadow
   Reorient_Trans(y, CamAxisDiff) 
   translate CamTarget
}

//a generic scene to vignette...
light_source { <100,100,-100>  rgb <1,1,1> }
plane { y, 0  pigment {  checker color rgb .5 color rgb .75 } }
sphere {  CamTarget, 2  pigment { rgb<0,0,1> }  finish  { phong .75 } }


-- 
@C[$F];
The Silver Tome ::  http://www.silvertome.com 
"You may sing to my cat if you like..."

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