Re: [photo-3d] First P3D use of term? (was Re: The Stereoscopic Society Annual Competitrion)

["John A. Rupkalvis" <stereoscope@xxxxxxxxxxxxx>]

----- Original Message -----
From: <chrisp@xxxxxxxxxxxxxxxxxxxxxxxx>
To: <photo-3d@xxxxxxxxxxxxxxx>
Sent: Friday, February 16, 2001 1:48 PM
Subject: [photo-3d] First P3D use of term? (was Re: The Stereoscopic Society
Annual Competitrion)


> Hello John
>
> Surely, since the stereo pyramid is the space where two separate lens
> pyramids coincide
>
> 1) the apex will never be at the lenses (unless they occupy the same
> space) but between and infront of them,
>
> and
>
> 2) the window can only be at one place on the pyramid, and to change
> the window (size or distance) you need to change the pyramid (by
> changing base, focal length, etc).
>
> Chris Pickering

I am not sure I understand what you mean by the space where two separate
lens pyramids coincide, since this actually only occurs at the plane of
convergence, which determines the stereo window.  This position can be
anywhere along the pyramid that the particular system is capable of
converging.  The apex of each pyramid is at the nodal points of the lenses,
but for practical purposes we usually consider one pyramid, and are usually
working with it some distance out from the lenses where the differences are
very small.  The stereo window can be anywhere along the pyramid that the
system is capable of converging.

> --- In photo-3d@xxxx, "John A. Rupkalvis" <stereoscope@xxxx> wrote:
> > The stereo pyramid is essentially an extrusion of the stereo
> window, such
> > that it describes the edges within which a subject must be without
> being
> > occluded at any distance.   Basically, the apex of the pyramid is
> at the
> > camera lenses (technically there are two pyramids, but since they
> are nearly
> > superimposed for normal stereo bases, we usually speak of it as a
> single
> > pyramid).  The base is at the farthest distance in the image.  The
> stereo
> > window can be anywhere along the pyramid from the lenses to the
> farthest
> > point in the background, and is determined by the plane of
> convergence.
> > Since the stereo pyramid is smaller closer to the apex, likewise
> the stereo
> > window is smaller, the closer it is to the camera.
> >
> > It is a useful construction when changing the distance from the
> camera to
> > the subject, since the edges define how close a subject of a
> specific size
> > can be before it is occluded by the stereo window.  For example,
> when
> > shooting an image of an actor poking a pole toward the camera, four
> C-stands
> > are set up with tapes running from close to the camera to the plane
> of
> > convergence, just outside of the photographable field.  These tapes
> visually
> > show the actor where the stereo pyramid is.  The actor then knows
> that the
> > pole will not touch any screen edge at any distance from the camera
> as long
> > as he does not move it too close to the pyramid edges as defined by
> the
> > tapes.
> >
> > A very good drawing illustrating the stereo pyramid appears on page
> 161 of
> > "The Theory of Stereoscopic Transmission" by Raymond & Nigel
> Spottiswoode,
> > University of California Press, Berkeley & Los Angeles, 1953.
> >
> > JR
>
>
>
>
>