[Bf-committers] Blender "lens" - Historic questions?

Ton Roosendaal ton at blender.org
Sat Nov 5 23:19:03 CET 2005


Hi,

As far as I can recall, it is based on the 640x512 aspect. Or PAL  
720x576.

The 36mm x 24mm aspect values, multiplied with 20 give 720x480, smells  
like NTSC to me!

-Ton-

On 5 Nov, 2005, at 15:10, Jonathan Merritt wrote:

> Hi Everyone,
>
> For basic renderings (without "parts" parameters or anything else  
> complicated), I've been able to establish the following relationships  
> between the "Lens" parameter (lens), horizontal FOV (FOVx) for the  
> Blender camera, and the image width (w) and height (h):
>    lens = (32/2) / ( tan( FOVx / 2 ) ),  for w > h
>    lens = (32/2) * (w/h) / ( tan( FOVx / 2 ) ),  for w < h
>
> Now, I've done some research on 35mm film.  My reading tells me that  
> 35mm is the vertical height of the film, /including/ sprockets.  The  
> actual exposed area of 35mm film is supposedly 36mm x 24mm.  Using  
> this fact, I get the following expression for FOVx in terms of focal  
> length (L) for 35mm film:
>    FOVx = 2 * atan( (36/2) / L )
>
> Notice the factor of (36/2)?  That looks similar to the factor of  
> (32/2) doesn't it?  In fact, if these factors were equal then the  
> Blender "lens" parameter would correspond exactly to the lens of a  
> 35mm camera.
>
> Now, the big question is: does anyone know why Blender uses a factor  
> of (32/2) and not (36/2)? :-)  I'm very interested to get to the  
> bottom of this, since information on both film sizes and Blender's  
> lens parameter both seem to be pieces of closely-guarded black magic!  
> :-)
>
> Jonathan Merritt.
>
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>
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Ton Roosendaal  Blender Foundation ton at blender.org  
http://www.blender.org



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