P3D The Third Deformation of the Third Dimension (1 of 6)

[abram klooswyk <abram.klooswyk@xxxxxx>]

This is my favorite deformation, because she demonstrates so
clearly the failure of mathematical (geometrical) theories
in accounting for some perceptual facts.
She also is charming in hiding herself in most cases, but
being predominantly present in a few other situations.
Moreover, in discussing her, I sometimes have had the
pleasure to meet people who deny her existence, and emotional
debates on such esoteric questions are of course among the
most rewarding ones :-).

Unfortunately I need some long postings to talk about her,
I don't have the time to formulate it shorter now.
In these postings I write mostly on Stereo Realist pictures,
but that is only because the Realist mounting system is a
good illustration of the principles, and it is of course on
the most widely spread stereocamera.
But the principles are the same for any system.

Bruce (making his own definitions) Springsteen wrote
(P3D digest 3569, 28 Oct 1999): (...)
>To me the word stretch is a very specific "deformation"
>(Ferwerda's term for deviations from orthostereo),
>related to angle of view (...)

To me stretch is just another word, meaning extend in length
or, for stereo, in depth. However, "deformation" for me is a
specific word, which has been used for over a century in
Dutch, German, and sometimes French, for space image
distortions in stereoscopy.
Ferwerda choose it for his English book too, after consulting
Dalgoutte, the stereo "Professor" from England, to avoid
confusion with "distortion", which is also in use as a term
for faults of optical images. Ferwerda followed a little book
published in 1945 by Berssenbrugge (a Dutch professional
stereographer) in his sequence of the stereo deformations.

George Themelis wrote (P3D digest 3573, 31 Oct 1999):
>Stereo photographers have readily identified this condition:
>B = Bv & F = Fv
>as ORTHOscopic STEREO.  If the stereo base is equal to the
>spacing of the eyes (roughly 65 mm) and the focal length of
>the recording lens matches that of the viewing lens then
>we perceive the stereo image in a way that imitates reality
>(viewing with bare eyes) as close as possible.
And:
>We have defined our three recording variables (F, B, I) and
>the way they affect the metric (measurable with a ruler)
>characteristics of the recorded image.  We have also defined
>our two viewing variables (Fv, Bv).

So where is the third viewing variable? The one comparable
to I (distance of the subject from the camera), but in the
viewing situation?
(To be continued)

Abram Klooswyk
===========