[photo-3d] Apparent vs. actual focus

["John Goodman" <jgood@xxxxxxxx>]

I've been exploring stereo projection, and can't quite pin down 
what my eyes are doing in terms of focusing. I see the screen 
acting as a window into the scenes, but the "depth" of the views 
beyond the screen plane appears to be about equal to my 
distance from the screen. For example, when the projector is 
10 feet from the screen and I'm viewing the screen from six 
feet away, the perspective of the stereo view seems to extend 
about six feet beyond the plane of the screen regardless of the 
image content, no matter if the infinity points represent objects 
that were 500 feet or 50 feet distant or, in the case of a macro, 
five inches. Of course the details of the scene make the 
interpretation of what I see appear pleasingly realistic.  

For increased viewing sharpness, I've been wearing prescription 
glasses behind polarizing glasses, and these have progressive 
focus lenses, from a near two feet at the bottom to infinity 
toward the top. As far as I can tell, regardless of the apparent 
depth of the stereo view, I'm focusing at or slightly beyond the 
screen plane, which makes sense, correct? What does theory 
say about this?

Thus there are usually major differences between the plane of 
physical eyesight focus during stereo projection and the planes 
of focus that existed in the photographed scene, not to mention 
corresponding disparities in convergence. I imagine that our 
visual system is adept at favoring the most apparent depth cues 
while ignoring conflicting factors. And experience increases 
one's ability to both create the illusion of realistic 3-D space 
while ignoring conflicting aspects?

John Goodman