P3D Re: "Too Much Depth" (was a lot of other stuff)

[Bruce Springsteen <bsspringsteen@xxxxxxxxx>]

Rumors of my demise are greatly exaggerated.  Al doesn't know the "angry
man" was a coward and fled when I quickly snapped him twice with my SLR. 
No prize.

A very interesting discussion has ensued about the nature of stereopsis in
the near range, most of which is over my head (the discussion, that is). 
Still, it seems intuitively plain to me, a simple geometer, that the
nearer an object is to you, the greater the retinal rivalries within that
object will become - and the greater the challenge of viewing it
stereoscopically will be - the reductio ad absurdum being the case of an
object at a convergence angle of 180 degrees (like a bullet between the
eyes X-( )where the object presents 100% rivalry to left and right views
and no points in common to fuse.  As we approach that limit, beginning say
within seven feet, it seems obvious that there will be some kind of
increasing strain in the act of cyclopean fusion - that still-elusive
process in the mind, after the eyes have done their thing.

But the question I hope we'll come back to is:  What is the source of all
this discomfort in "too much depth", really?  Is it the extreme changes in
convergence between near and far parts of the scene and the muscular
workout involved?  Is it the introduction of wider angles of convergence
in the near range with attendant loss of fusible material for the mind to
work with?  Is "limit your depth" a warning more related to non-ortho
viewing of projected material, in formats with a seven foot window
imposed, worsened by misguided attempts to widen infinity separation
beyond interocular size in viewing?  We tolerate a full range of depth
fairly well in direct vision, why does the whole thing go bad in
stereography?  Seems to me that if all the angles are ortho, there should
be at least no more discomfort than in reality.

Some suggestion has surfaced that inability to fuse all parts of the scene
*at once* is the problem, but that is never done anyway - and diplopia
(the doubling of objects not currently fixated) is probably a helpful,
even essential, cue in stereoscopic perception.  I don't believe that
that's the problem.

If this question is answerable, I expect it to be a simple and obvious
answer.  I'll try to read the literature on vision, though, as time
permits.

Bruce 



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