[Sidefx-houdini-list] aperture focal length relations

Adrian Lee dryrainstudios at gmail.com
Thu Jun 21 12:35:09 EDT 2007


for any one following this I found a nice little webpage that works out the
angle of view for you

http://www.mat.uc.pt/~rps/photos/angles.html



On 21/06/07, Rangi Sutton <rangi at kanuka.com.au> wrote:
>
> Mario Marengo wrote:
> > On June 20, 2007 01:10 pm, Adrian Lee wrote:
> >
> >> trying the aperture thing out and with the values of:
> >>
> >> resx 1024
> >> resy 1024
> >> ratio 1
> >> houdini units 1 = 10mm
> >> and a given focal length of a film lens of 21mm
> >>
> >
> > A 21mm prime lens (and 35mm film) has a horizontal angle of view of
> about
> > 81.47 deg. (based on interpolation between 20mm and 24mm Canon lenses).
> So,
> > assuming fovx=81.47 is somewhat in the neighborhood, then you can set
> > Houdini's camera as follows:
> >
> > focal = 21
> > aperture = 2*ch(focal)*tan(81.47/2) = 36.1704
> >
> > Now create an object with a unit grid on the XY plane and parent it to
> the
> > camera. Translate it by -21 units in Z, and scale it by 36.1704 (the
> > aperture). It should fill your 1024x1024:1 frame exactly.
> > However, whether this setup matches your plate depends on how accurate
> the
> > (assumed) horizontal aov of 81.47 deg. is and on whether you're looking
> at a
> > full-aperture image or at some kind of cropping.... things definitely
> can get
> > messy with all this stuff(and I'm certainly no expert on any of it).
> >
> If you're no expert then I'm afraid the rest of us are total ignoramus.
> I think you've added a page to more than a few wikis around the world
> just then... ta.
>
> ta.
> r.
>
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