> Should make a camera with a field of view of 90 degrees. Now, if I am 
> correct so
> far, then Povray will create the <right> and <up> vectors to satisfy the 
> default
> aspect ratio. For an output image of 640x480, This would imply that each 
> pixel
> (square pixel) will have a side that is (1unit/640) or 0.0016 units/pixel.
> However, from other computation that I am doing, it seems I am making an 
> error
> with my calculation of the pixel width of the image. Does this seems 
> correct or
> am I doing something wrong?

The default right vector is 1.33*x to match a common aspect ratio, but
it doesn't change automatically if you use a different aspect ratio.
I like to use
right     x*image_width/image_height
in my cameras just because of that.

This also means that the default horizontal FoV angle is 67.38 or so,
if you want to control the horizontal FoV angle with the direction
length, just set the aspect ratio with "up" instead of with "right".

camera { // a camera with 90 degree horizontal FoV
   location <0,0,0>
   direction 0.5*z
   right x
   up 0.75*y
}

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