Meaning of distances in stereo talk

[P3D Paul Talbot <ptww@xxxxxxxxx>]

We often hear of the built-in 7 foot window of the Realist, and
phrases like the "nearest object" or "farthest object" in the
scene.  But how are distances measured for these purposes?
Point to point?  Or is it based on the distance between the film
plane and a parallel plane?

An example:  A tall person holds their Realist at eye-level, 6 feet
above the ground.  An object in the scene lies on the ground such
that a plane parallel to the film plane, and passing through the front
edge of the object, is 6 feet away from the film plane.  The
front edge of the object, however, lies more than 7 feet from the
image it creates on the film at exposure.  (I hope I didn't screw
up on the geometry!)  In the real world, such an object would be
in front of a window that lies parallel to the user and 7 feet away.
But the object is more than 7 feet from the film plane, so a
casual reading of the workings of the stereo windows suggests
the object would appear behind the window (assuming "normal" chip
spacing).  Thoughts from the technical experts?

Thanks,

Paul Talbot


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