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Re: Effects of lens length
> > question - if you did this, would you have the same stereo image
> > as if you had shot both sides with lenses of the same FL? That is-
> > if you crop an image taken with a 50 mm lens to the same part as
> > an image taken with a 80 mm lens, and make them the same size - would
> > you have the same thing as two pictures both taken with 80 mm lenses?
> >
> No. The length of a lens impacts the relationship of foreground and
> background objects. There is a famous shot in the movie Jaws (which
> has been copied by many others since) in which the camera started on
> a shot of Roy Scheider at a fairly wide-angle setting of a zoom
> lens. As he realized that the shark was attacking, the camera was
> pulled away from him quickly, and the lens zoomed in toward him at
> the same rate. The result was that the actor appeared not to change,
> but the background seemed to rush up toward him. As the lens became
> longer, in effect, the relationship between the foreground object
> (the actor) and the background appeared to compress, and the effect
> was heightened by the camera movement and the zoom counteracting
> each other to give the appearance that the actor did not move. I'd
> guess this effect would seriously harm the stereo effect in the
> hypothetical situation you suggest.
I believe Hitchcock used this technique, in reverse, in "Vertigo."
There's a shot from the top of the bell tower looking down in which
the camera tracks while the lens zooms from long to short focal
length, giving the effect that the tower is elongating.
-pd
--------
Peter Davis "Education is not the 617/873-4145
BBN Educational Technologies filling of a pail, but FAX: 617/873-2455
70 Fawcett Street the lighting of a fire." pdavis@xxxxxxx
Cambridge, MA 02138 -- W. B. Yeats
URL: http://copernicus.bbn.com/people/PDavis/
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End of PHOTO-3D Digest 1503
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