Re: 3-D phenomenon

[P3D Gregory J. Wageman <gjw@xxxxxxxxxx>]

Jim Crowell writes:

>Actually, that's not quite right; when you look at objects at
>different distances in a stereo view, the convergence angle of
>your eyes changes but the focal length of your eyes' lenses
>(your accomodation) doesn't.  It's generally believed that
>aoccomodation is only useful as a depth cue out to about 2
>meters, though, & even there it's pretty weak.

Are you certain that it (accomodation) *never* occurs, or is it
that it doesn't *normally* occur because the "typical" realist slide
(if there is such a thing) has most of its subject of interest beyond
the distance where such accomodation is necessary?  Considering that
the window is at about 2 meters this would be consistent, no?

I ask because with the one or two slides I have that have *very*
close *and* very far subjects, it sure looked to these eyes like my
focal length was changing along with the convergence angle in order
to view the nearest object.  I think it was this that made them so
uncomfortable to view, because the distances weren't natural (ortho).

I agree that with a "typical" slide where most everything is behind
the window, no accomodation occurs and everything remains sharply
focused if it is so in the slide.

	-Greg


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