Re: Meaning of distances in stereo talk

[P3D John Bercovitz <bercov@xxxxxxxxxxx>]

Paul, I'm not 100% sure I understand your question but that won't
stop me.  8-)  Yes you do measure the shortest distance between
parallel planes, which is a distance perpendicular to both planes, 
because a camera is a plane to plane device and in the present case, 
is a plane to parallel plane device.  The window distance is 7' away
but the window is a plane also so parts of it are farther away than
7'.  And you're right, most cameras are calibrated for distance 
from the film plane because the film plane doesn't move when you
focus but the lens does.  In most cases this doesn't matter because
the lens is so short (say 35 mm) compared to the distance from the 
camera to the scene.  If you get into larger format stereophotography, 
you'll need to start figuring from the locus of the center of perspective.  
(The C of P is at the entrance pupil of the lens.)

John B



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