P3D PePax challenge # 1

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

After I fire this trilogy, I promise to be quiet for one week! :-)
Mark asked questions related to PePax principle.  Earlier I posted
a challenge on how to explain this principle with simple and
intuitive terms.  Here is my entry:

Q:  Why do we need long focal length (telephoto) lenses in stereo 
    photography?

A:  For the same reason we need them in flat photography:  To produce 
    a magnified view of a portion of a scene.  To give the illusion 
    that we are closer.  To allow us to record details or photograph 
    distant objects.  Examples:  Portraits, close-ups of animals 
    (especially wild!), architectural details, far away action (sports) 
    or objects (moon), etc.

Q. What happens when we use long FL lenses but keep a normal stereo 
   base?

The scene appears to be lacking depth.  Judging from the size of
objects, the brain thinks that we are closer to the scene that we 
really are.  But the depth in the scene is not aa much as it should 
have been if we really were closer.

One example is using binoculars.  They offer a magnified view but a 
stereo base close to normal.  There is a lack of depth in the image.

One result of this lack of depth is the well-known "cardboard cutout" 
effect where people (usually, could be animals too) look like 
cardboard cutouts instead of real people.  This is happening because 
we see that different objects are in different depth levels while we 
do not see depth within individual objects.  The "cardboard cutout" 
effect is intensified by the lack of motion (in a still 3d picture) 
and the presence of depth and comparison with real life.  For example, 
no one seems to complain about cardboard cutout effect when using 
binoculars (where there is real live action) or when looking at flat 
pictures (because we have been conditioned to interpret flat images) 
but the presence of depth, frozen motion and strong resemblance to 
reality brings such complains for stereo pictures.

To be continued....

George Themelis


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