Am 02.05.2010 16:43, schrieb POV-Zhstar:

> scene by POV-Ray. Because the field of view of the camera is 25 degrees and
> POV-Ray uses the reverse ray tracing (rays are sent backwards from the camera to
> the light source), then I thought the output scene should be a circle for this
> case (camera vertically sees the object plane), ellipse otherwise. But the

> this. Could someone explain the reason? Thanks!

The "angle" keyword is intended to be used for "zooming" in on an image 
without having to fiddle with the other camera parameters - and that's 
all it does. The value you specify here will be the /horizontal/ opening 
angle of the camera frustrum, which will remain pyramidal in shape 
(typically with a rectangular base) at least with the standard 
perspective camera, i.e. the image will remain rectangular.

If you need a circular-shaped image, you'll need to post-process it in 
your favorite image manipulation software.

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