[Sidefx-houdini-list] aperture focal length relations

Adrian Lee dryrainstudios at gmail.com
Wed Jun 20 14:53:14 EDT 2007


ahhh using pre known aov is where I was going wrong, (well one of the
places) I thought the aov would be of the digital sensor. I'm sure I can
find a list or coralating  lens to  aov in American cinematographers

Thanks muchly

Ed

On 20/06/07, Mario Marengo <mario at axyzfx.com> 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).
>
> HTH.
>
> --
> ......................................................................
> Mario Marengo                                  mailto:mario at axyzfx.com
> AXYZ ANIMATION                                 http://www.axyzfx.com
> ......................................................................
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