Am 23.10.2013 16:11, schrieb Ingwer:

> you are doing a great job. but I have a question about the aperture.
>
>> apertureDiameter = focal_length / fstop
>    (fot real camera this is 100 percent correct)
>> aperture (apertureDiameter / focal_distance) * 1000
>    this is what I am looking for. but where did you get this formula? I look up
> the Povray reference, hut there is no such a description. Can you tell me the
> principle or theory?

Edouard already corrected this; it has to be:

 >>    aperture (apertureDiameter) * 2  // Magic Number

The magic number is simply that: Magic. It appears that when the focal 
blur code was originally implemented, the "aperture" parameter was 
intended as nothing but an artificial dimensionless value to control the 
amount of blur, and that it just happens to be twice the aperture diameter.

(Alternatively, it might be that the original author intended it to be 
the aperture radius, and got the scaling factor wrong way round. Or it 
was intended to be the aperture radius, and the scaling factor was 
erroneously applied twice. At any rate, for compatibility reasons we're 
now stuck with this parameterization.)

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