P3D The Third Deformation of 3D, The third variable (2 of 6)

[abram klooswyk <abram.klooswyk@xxxxxx>]

Where is Dr.T.'s third viewing variable? I suppose the dear
Dr. would say: that is just the unknown we are looking for!

Right, but there is more to it, there really is a missing
variable, the two conditions B = Bv and F = Fv are *necessary*
but not *sufficient* conditions for Orthostereoscopy.
A third condition relates to convergence.

Now convergence is an often misunderstood term in stereo,
which is explained by the fact that it has at least three
different meanings.
1. Convergence of the optical axes of two cameras.
   (This better is called toe-in, not convergence)
2. Convergence of the eye axes. This seems clear enough.
3. Photographic Convergence.

You can draw two imaginary lines from the lenses of a
stereocamera (or of two aligned monocameras) to an object in
the scene to be (stereo) photographed. These lines converge
to the object. We can imagine these lines as the "viewing
lines" of the lenses (they are not the optical axes).
The convergence angle of these lines is different for objects
at different distances. This is Photographic Convergence.
At infinity the photographic convergence angle is zero.
Using a 5P camera (Stereo Realist type, lens separation
70 mm) the photographic convergence at 7 feet is about
two degrees.

So we are at the angles again, from where the deep insights
mostly come :-).
(To be continued)

Abram Klooswyk
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