P3D Re: Keystoning - mea culpa

[aifxtony@xxxxxxx (Tony Alderson)]

Gabriel Jacob wrote (digest 3429):
>P.S. It's interesting to note, that the philosphy in 3-D movies is to
>converge the cameras (I'm not sure about Imax though). The effects are
>supposedly minimal, which might be true for movies but not for still
>photography.<

IMHO, this practice is common in stereo cinematography for economic
reasons. It is easier to adapt existing monoscopic equipment by using
toe-in than to build stereo movie cameras. The primary other option is to
optically print the entire film to offset the images into a stereo window.
This is expensive and has it's own problems.

The results of toe-in are the same as in still photography, stereo cine
system promoters are simply making a virtue out of necessity. Personally, I
think the effects of toe-in are potentially worse in motion pictures, as
there is less "wiggle room" (I think Klooswyk called it "tolerance"). In
films, at least, you have a base level of eyestrain from things like
projector weave, so I feel keystoning contributes to the bad reputation of
3D movies. (Bad projection is a worse problem...)

Not all stereo movie systems use toe-in in photography, however. The
Stereovision over/under lenses do not toe-in; it has shifting lens elements
to converge the stereo image without keystoning. IMAX does not toe-in, but
they put infinity points at the screen plane on projection.

Tony



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