P3D Hypo - Ortho - Hyper OR convergence angle?

["Dr. George A. Themelis" <DrT-3d@xxxxxxxxxxxxxxxxxxxxxxxxxxx>]

Larry asks:

>why pay all this attention to the terms Hypo, Hyper, and Ortho at all? 

Because they are derived from Greek roots?  :-)

Hypo:  under
Hyper: over
Ortho: correct

These terms just cover general situations.  They give us some idea of 
the subject matter and the way it was recorded.  For me, Ortho are all 
my Realist shots.  Hypo are my macro shots using my Minolta macro 
lens.  Hyper is single or twin SLR stereos with increased base.

How about the terms "wide", "normal" and "telephoto" used to classify 
lenses?  These seem arbitrary to me too.  If you view a picture taken 
with a wide angle lens close enough or one taken with a telephoto from 
a distance you get a "normal" perceptive.  But this is a way to classify
a lens and also you get an idea of the effect if the images are viewed
from a constant distance (or FL lens, etc.)

>Consider that for ORTHO pictures with a stereo camera, the ideal subject
>distance is around 7 to 15 feet. That represents a finite range of
>convergence angle. That *identical range* of convergence angle is needed
>for either a Macro, or Micro or a Hyper distant scene of mountains to 
>appear with satisfying depth relationships.

Hmmm... I don't agree with this statement... "Satisfying depth"?

Let's see... A subject at 7 feet (2130 mm) is at a convergence angle of
2* invTan(70/(2*2130)) [70 mm is the lens spacing in the Realist]
which is 1.9 degrees.  That's a small angle.  My SEM stereopairs are 
recorded using at least 6 deg. angle tilt.  Yet both appear to have 
"satisfying depth relationships".  

There is more to depth than convergence angle.  The overall depth 
variation (roughness) is a factor too.  I tend to believe that the
only thing that counts for non-ortho situations (excuse me but I have
to use this term to mean situations that cannot be seen with bare
eyes) is the on-film deviation.  This needs to be restricted.
Different subjects will require different convergence angles to
give the same on-film deviation.

>Getting a good stereo image depends far more on achieving
>a suitable convergence angle (enough but not too much) than it does
>on staying near the normal interocular distance. The appropriate 
>convergence angle applies continuously and equally to the entire 
>scale from Electron Scanning Microscopes to Telephotos of the Moon. 
>It is a much more applicable detail with real meaning.

OK.  You can classify your images according to their convergence 
angle.  I will continue to use the terms "Hyper", "Ortho" and "Hypo" 
that give me a better idea of the subjects and the tools used to 
record them.

George Themelis


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End of PHOTO-3D Digest 2438
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