Re: 3-D phenomenon

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

Allan Woods writes:

>I might add that I think the reason people go "Ahhh!" when they see
>a projected 'Realist' slide is precisely because it "looks" like
>3-D but over-emphasizes one clue channel and disregards the rest.
 
>It is precisely this imbalance of input which carries the impact.

I don't entirely agree with this.  I think you're overstating the
importance of selective focus (DOF) versus binocular disparity.

When I look out a window at a distant scene, I see depth, yet all the
objects are in focus.  I find just by looking out the cubicle in which
I now sit that things beyond about 10ft away are in focus.  I
still must converge/diverge to fuse nearer/more distant objects, but
the one doesn't go out-of-focus when de-fused.  I verified this by
reading a poster on the wall while diverging my eyes as if looking at
a much more distant object, a trick learned from viewing stereo images!

For extremely close objects this doesn't maintain; if I fuse a finger
held about a foot from my face, the background is both doubled and
out-of-focus.  However, most projected Realist slides (not macro slides)
are more like the 'view out of the window' case; since the stereo window
is at roughly ten feet and typically all objects are behind it, it is
not strange at all that they should all be in sharp focus.

Besides, it *is* possible to focus on the subject and deliberately blur
the background without lessening the "Ahhh!" factor. :-)

For me, the impact of stereo projection is related to the illusion of
depth "into" and "out of" a screen known to be a flat plane.  And even
though it is frowned upon by others, I also really like slides where the
foreground subject appears to come through the window, as long as no part
of it is cut off at the window's edge.  This is trickier to do in reality
than it sounds, and I often fail to notice something close getting cut
off while framing a shot.  It is then that I understand why this is a
no-no, as these are murder to view when projected. :-)

	-Greg




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