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

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

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

----- Original Message -----
From: "Paul Talbot" <list_post@xxxxxxxxx>
To: <photo-3d@xxxxxxxxxxxxxxx>
Sent: Thursday, February 15, 2001 9:57 AM
Subject: [photo-3d] First P3D use of term? (was Re: The Stereoscopic Society
Annual Competitrion)


> "John A. Rupkalvis" wrote:
>
> > If the subject is large and/or close, such
> > that parts of the subject are occluded by the frame edges, you must
consider
> > the stereo window, the stereo pyramid...
>
> I'm approaching my five-year anniversary of joining this list, and I
> do believe I have never heard the term "stereo pyramid."  Nor can I
> find reference to it in searching the archives on Marco's site
> http://www.pauck.de/archive/mailinglist/photo-3d/photo-3d.html
>
> Please elaborate on the term, John!
>
> Paul Talbot
>
>
>
>