P3D VM Virtual Viewer and The "Stereo Window Position"

[Bruce Springsteen <bsspringsteen@xxxxxxxxx>]

Despite his fatigue the other night, Gabriel correctly summarized the
issue of interpupillary distance and viewer lens size, if I recall a
discussion we once had about View Master and children.  My memory tells me
Abram and I were negotiating our estimates of what range of interocular
distance a typical VM viewer could serve, without losing part of the image
on the outside (for wide-eyed folks) or the inside (for small IO folks
like Paul Talbot).

This all has to do with the collimating function of the viewer lenses.  If
the optical center of each lens is aligned with the central perspective
point (call it "infinity center" if you like) of its film chip, then no
one will have divergence problems, because all parts of the focussed lens
redirect a ray from the image to emerge at the same angle as it would when
viewed through the lens center.  (There's a convoluted sentence - parse
that!)  So infinity will be at zero convergence no matter what part of the
lens you look through, no matter how far apart your eyes are, as long as
the lenses are sufficiently large for you to see a whole image in each.

The interocular adjustments on viewers, not for interpupillary matching
purposes at all, are equivalent to the horizontal adjustment on a
projector - they move this "infinity center" off your center of vision,
either making you diverge infinity and creating frustum deformation away
from you, or making you converge infinity and creating frustum deformation
towards you.  The mind simplifies what it is seeing and says the scene
"moved away" or "came closer", but it is really more complicated than
that.  This is what people are really seeing in Krause's (Freudian) cannon
gag.

In no case described above is the scene moving relative to the stereo
window, as George noted, and which was the original question of
demonstrating stereo window control when cropping or mounting.  This
distinction is important to understand.

Best wishes,
Bruce 
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