P3D the world is non-ortho

[Peter Abrahams <telscope@xxxxxxxxxx>]

Re: world of non-ortho
>> Instead of striving for ortho stereo, why not use the 
>> energy to explore the endless world of non-ortho stereo?  
>I'm curious; what do you mean by non-ortho?  Which of the
>non-ortho effects is that you like?

I like a little hyper in my photos, increased sense of depth draws me into
the scene & 'makes me feel like I'm there'.  I also like to manipulate the
placement of the photo in the window.
Those of you who spend lots of time at stereo photography might like a flat
scene to look flat in a photo, but if it looks as good in a flat shot, I'd
rather not go to the trouble of mounting, etc.  Of course, hypers of
landscapes & hypos of bugs are 'correct' uses of non-ortho, since only the
perceived distance to the object & its size are changed, not its geometry
(shape & arrangement in environment).

But more than that, I'm an ortho-atheist.  I like to keep orthostereoscopy
in mind without 'believing in it'.  One doesn't violate ortho for an
effect, it is violated because it is not inviolate.

The Zen of Ortho:
An individual can reconstruct the geometry of real objects in the world, in
a stereo photo that places those objects in an arrangement where the
perceived distance to the objects, the angles between the various objects,
and the sizes and shapes of the objects, all match the view of the real
world.  For an individual stereoscopist, orthostereoscopy is possible.
However, once we start sharing our stereo photos, ortho is an average or
compromise.  There are significant differences between individuals in the
psychological & physical capacity of our natural stereoscopic equipment.
Perhaps it isn't correct to compare someone with a highly developed mental
capacity for stereo, to someone that is stereo impaired, and claim that an
orthostereoscopic reconstruction for the one would be much different than
for the other.  (It might be, but I'm not going out on that limb yet).
But our physical equipment for stereo vision is far from standardized.
Interpupillary distances range from 80mm (I've read that Hawaiians have the
widest IPD of the races), to a child's IPD, somewhere in the 40mm range.
This would cause a large difference in convergence angles for nearby
objects.  
Is the range of focal lengths of the eye large enough to have an effect
here?  Certainly the focusing ability of individual varies tremendously.
If you can converge to a near point, but can't focus to that point, then
stereo photographs might give you a sharp view of near objects, which would
look something like a window violation if you weren't used to it.
Nearsighted people use spectacles with prismatic, diverging lenses.  This
would certainly effect perception of the placement of objects.

The differences between a view and a photo also mean that an ortho
reconstruction might not use an exact geometry.  The eye might see contrast
where the film cannot, and the increased detail your eye is seeing, that is
invisible in the film, might mean that an effectively ortho photograph
would need enhanced depth.  Or, film can certainly see detail in dim light
that the eye cannot, and a long-exposure stereo might show all kinds of
depth in a sunset shot that the eye would miss.  Dusk does seem kind of
flat, so should a stereo photo of dusk have reduced disparity to match it?

(BTW, even the apostles of ortho on this list have approved its desecration
under many circumstances, so I'm not saying they should be put to the lions
or anything.  Actually, I'm writing an essay on stereo optics for our
Cascade Stereo Club's first annual show, or rather avoiding writing it
right now.  I'm hoping that any flaming errors will be corrected in our
nice private list before they get out to the public.)
_______________________________________
Peter Abrahams   telscope@xxxxxxxxxx
the history of the telescope, the microscope,
    and the prism binocular


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