[Sidefx-houdini-list] aperture focal length relations

Mario Marengo mario at axyzfx.com
Wed Jun 20 10:56:40 EDT 2007


On June 20, 2007 08:29 am, Adrian Lee wrote:
> Hello back again and still trying to match move Houdini's cameras.
>
> Does anyone know the relationship of aperture to the focal length in

Open up the on-line help and search for "world camera". Near the top of the 
results should be a document called "Match Houdini camera lenses to the real 
world". This has all the relevant information regarding how focal length and 
aperture are related in Houdini. Like Jeff, I also think Houdini's "aperture" 
is closer to "film aperture" -- geometrically: a 1-unit-wide object placed 
focal_length units in front of the camera will project to an aperture-wide 
object on the image plane (i.e: the entire with of the image on the "film").

The page gives the basic relationships, from which you can derive anything you 
want. Here are some more relations (BTW: another misnomer in the following is 
"fov", or "field of view", which should really be "aov" or "angle of view"):

fovx = 2 * atan(apy/(2*focal))

fovy = 2 * atan(apx/(2*focal))

apx = 2 * focal * tan(fovx/2)
or
apx = (aspect * apy * resx) / resy

apy = (apx * resy) / (aspect * resx)

...


HTH.

-- 
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Mario Marengo                                  mailto:mario at axyzfx.com
AXYZ ANIMATION                                 http://www.axyzfx.com
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