Parallax differences...

[P3D <LeRoyDDD@xxxxxxx>]

... are the primary determinant in stereopis. Well, to be exact, the rapid
comparison of parallax differences.

     I am convinced by the following "proofs":

Fix your gaze on an object... do not move your head!... do not shift your
gaze from the object! As you are able to become aware of the rest of the
scene without shifting your gaze, you notice the other objects in the scene
are doubled and the only depth visible is because of the secondary cues...
known size, overlapping objects, etc. This exercise can be really hard to do
and feel quite unnatural(it is).

Pseudomount a 3-D image with *strong* "secondary" depth cues. The secondary
cues are overidden by the now-reversed parallax differences.

Mount a closeup taken with regular lens spacing of a known object at two to
three feet in a "closeup" mount. This changes the viewing convergence to that
of an object at six to seven feet. Most observers don't see a big object at
six feet as in a reduced lens spacing closeup or interpret the far part of
the image... a rose stem, perhaps... as actually being near infinity. They
may feel a sense of unease due to seeing a "close" object with weak
convergence, but in a dark viewer or a truly darkened room, this is minor.

     Actually, I haven't projected the last instance recently, so other
listers can confirm or comment on their experience.
     I prefer to mount an image like this in a "normal" mount and mask down
non-analogous image content. This restores accurate convergence... but if you
don't have control of a projection show, the person on the controls is apt to
curse, mildly or not depending on their inclination, and superimpose the
mount apertures, which will give the effect of having mounted in the closeup
mount, anyway.

LeRoy Barco
LeRoyDDD@xxxxxxx


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