Gentlemen,
 I need to be convinced that the camera projections used in POVRAY  are
meaningful.   A normal distortionless lens gives an image height defined by
the product  focal length  x  the tangent of the field angle.  Very wide
angle lenses must have high distortion to create a finite image height.
Typically a very wide angle lens creates an image height proportional to the
paraxial focal length and the field angle itself.    The 'fish-eye' camera
in  POVRAY seems to be a rectangular image projected onto a sphere  hence
the circular image.  This is not a fish-eye lens.

Comments, please

Don Barron

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On Mon, 28 Jun 1999 21:08:48 +0100, Don Barron wrote:
>The 'fish-eye' camera in  POVRAY seems to be a rectangular image 
>projected onto a sphere  hence the circular image.  This is not 
>a fish-eye lens.

I'm not sure how you could have reached this conclusion.  First,
a simple scene that demonstrates that it is not in fact a mapping
from a rectangular image of any sort:

camera {
  location  0
  direction z
  angle 120
  fisheye
}

light_source { 0 color rgb 1 }

#declare i=0;
#while (i<360)
  sphere { 40*z, 1 rotate i*y texture {pigment {color rgb 1}}}
  sphere { 40*z, 1 rotate i*x texture {pigment {color rgb 1}}}
  sphere { 40*z, 1 rotate i*x rotate 45*z texture {pigment {color rgb 1}}}

  #declare i=i+10;
#end

If this were a rectangular image mapped into a circle or sphere or
whatever, one would expect more spheres to appear on the diagonal.

Second, you need only read the source code, which is freely available
whereever you got POV-Ray, to verify that the fisheye camera in fact
maps a portion of a spherical image onto a rectangle, just as a real 
fisheye lens does (though there does appear to be a bit of weirdness 
with the aspect ratio.)

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