Effect of pseudo-stereo

[P3D <PTWW@xxxxxxx>]

Now that the topic of pseudo-stereo is on the board, here a couple
questions I have been puzzling over.

First, I once did some experimenting with viewing 2x2 pairs (aerial
hypers) in pseudo-stereo.  I perceived 2 different effects, depending
on the particular image pair.  Two specific examples stand out in my
memory because the effects were so different.  With one pair, the image
seemed totally flat when the left and right slides were reversed.
Alternating between one-eyed and two-eyed viewing did not cause any
particularly noticeable changes in my perception of the image, although
the same exercise clearly revealed depth when the images were in their
usual arrangement.  With the other pair, swapping left and right images
caused an obvious rearrangement of objects along the z-axis: objects
that had been in the background now appeared to be in the foreground.
Is this perceived difference more likely attributable to technical
differences in the the recording of the stereo information on the film,
(amount of on-film deviation; location of objects on the z-axis, etc.)
or to differences in the brain's willingness to perceive the subject
"inside out?"  (Hint: one scene was all solid fixed objects, the other
was a volcano with clouds in the sky, in which background clouds became
foreground clouds in the pseudo view.)

Second, how does one determine by looking at the two chips of a pair
which is the left and which is the right, assuming there are obvious
edge objects toward the foreground?  If I create a stereo pair with
the shoot and shift method, carefully guarding against any toe-in,
an object on the left edge will start to slide out of view when I
move the camera to the right for the right image.  This seems perfectly
logical.  However, I have commercially mounted Realist pairs in which
the right-side view seemingly captures *more* of an object on the left
edge than does the left-side view.  Yet there is no evidence of a
pseudo-stereo effect when viewing the pair.  Why do the two situations
seem to produce differing results?

Paul Talbot


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