Le 05/09/2013 11:53, timer a écrit :
> Le_Forgeron <jgr### [at] freefr> wrote:
>>
>> First, it depends on the type of camera to take into account or not the
>> length of the direction vector, and usually it's a ratio with the
>> other(s) vector(s) (up/right)
>>
>> Second, not at all.
> 
> 
> It is an perspective camera an the ratio from it is 4:3 which is also the
> standard ratio for povray.

Then, the relation between direction, right and angle is as follow:

direction.length := (right.length / 2 )/tan(angle/2)

How you convert a focal length to an angle of view is left as an
exercise for the reader:

The now historical 24mmx36mm film format has a diagonal of 43mm, and a
"normal" lens has a 50mm focal length, for an angle of about 53° on the
diagonal (whereas povray use the angle on the horizontal)

tan(53°/2) = sqrt((right.lentgth/2)²+(up.length/2)²)/(direction.length)

the interesting part is reaching 53° from 43mm of film diagonal and 50mm
objective. (some magic is needed, such as a 43/50 ratio on the objective
length)

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