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

[chrisp@xxxxxxxxxxxxxxxxxxxxxxxx]

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



--- 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