Re: understanding...

[P3D Jim Crowell <crowell@xxxxxxxxxxxxxxx>]

At 12:07 9/19/96, P3D John Bercovitz wrote:
>Allan writes:
>> John, rhetorically, why can't you take a stereo pair of something
>> close to the camera and include something in the frame which
>> is apparently at infinity? I can see that with my eyes and look
>> near, then far?
>
>But to answer this latest of your questions first, I don't know why you
>can't go from closeup to infinity in one stereo pair.  I only know that
>the thing will start to dissociate if you try to shoot it with a normal
>stereobase.

It's a good point; in daily life you are constantly faced with a range of
disparities greater than the fusional range, yet it's not as annoying as a
stereoview with a large range of disparities.  A couple of hypotheses:

1) unless you mount to infinity, there's a good chance that the either the
most distant points will be beyond the infinity vergence point or that the
nearest point will be require a great deal of convergence.  Either of these
situations might lead to discomfort.

2) Looking at a stereoview, your eyes have to focus at a fixed distance.
As you look at near & far points in the picture, your eyes converge &
diverge.   Because convergence & accomodation are linked, this tends to
drive the image out of focus & you have to expend effort to counteract this
tendency.  The greater the range of disparities, the more the effort on
average that will be required & the greater the fatigue.

-Jim C.

----------------------
Jim Crowell
Division of Biology
216-76
Caltech
Pasadena, CA
(818) 395-8337
jim@xxxxxxxxxxxxxxx



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