In article <3fa3bac8$1@news.povray.org>,
 "Fab" <--fab### [at] u-picardiefr--> wrote:

> in optic, if the radius is 250, the cylinder should NOT fills half the width
> of the image.
> 
> if I wished to fill half of the image, I need a radius of   tan ( 90 / 4 ) *
> 499
> and that's not the case with povray.

I think you're misunderstanding the projection or the math. What you are 
doing is projecting a 2D plane (that of the end of the cylinder) onto 
another 2D plane (the image plane) through a pinhole camera. If you 
double the radius of the cylinder, the apparent radius of the cylinder 
will double. The radius you need to fill the image is tan(90/2)*499, 
which happens to be 499. To fill half the image, you need 
tan(90/2)*499/2.

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

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