Le_Forgeron <lef### [at] freefr> wrote:
>
> 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)

Thanks for explaining, you helped me a lot.

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