re: focal lengths

[P3D Section of Epidemiology <dworrell@xxxxxxxxxxxxxxxxxxx>]

>Ray Hannisian>If using a higher focal length simulates
being closer to an object, should 'zooming in' require an
increase in the distance between the cameras (to simulate
the 'line of sight' angles for a person actually standing
closer to the subject)?

I've often wondered about this myself. It seems to me that
the "convergence of parallel cones of vision" (I hope that
term accurately describes the idea, we had the
convergence/toe-in discussion a few weeks ago) would extend
to infinity.

>John B>Actually, using a longer lens doesn't simulate
being closer to an object unless the object is flat.

Huh?

>John B> ... increase the focal length of the camera's
lenses to 100 mm and also increase the focal length of the
viewer's lenses to 100 mm, there is no net effect on the
reconstructed space.  However, if you use long lenses to
take the picture and short lenses to view it, the depth
will be flattened. Increasing the stereo base results in a
"hyper" view which decreases all dimensions of the
reconstructed space equally.

Shouldn't longer lenses limit the hyper-stereo effect when
shooting landscapes and subjects at a distance? And the
hypers I've seen don't seem "flattened" just "shrunken"
which is what you're saying, but why don't they get flat at
a distance like "standard" 3-d? Some of the Cloud hypers in
photo 3-d seemed to have depth all the way to infinity.
Perhaps I'm confused ... (so what's new?) Please help me
out here.

I'm very interested in shooting wildlife in 3-d, but it is
usually difficult, often impossible and occasionally
dangerous to get close enough to use "short" lenses. And
"Brown Dots" (Was that dot a bear or a moose?) are just as
uninteresting in 3-d as they are in 2-d. Realistically
200mm is "short" for wildlife photography 500mm is average
and the "pros" range up to 1000mm ... (I got major "lens
envy" over a couple Leicas with 1000mm lenses last year at
Katmai, the bear place.) Does that mean I'll have to have
Dr. T make me a custom Red Button with 200mm lenses? And
custom lenses for projecting?
_______________________________
Dave Worrell
State of Alaska
Section of Epidemiology


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