Re: focal lengths

[P3D Dr. George A. Themelis <fj834@xxxxxxxxxxxxxxxxxxxxx>]

>Here is a practical example: I took a stereo portrait of my children with
>135 mm lenses in side-by-side SLRs.  The longer FL and increased lens
>distance are trying to simulate being closer to them but, when I looked
>carefully at the picture I noticed that their nose looked compressed and their
>ears enlarged.  If I had come closer, the nose would become larger compared
>to the ears which are further away.

I should add here that I had not noticed these distortions until I entered
these pictures in the Gamma SSA folio and Dr. Milligan pointed them out. 
With his comments in mind I looked again and there were present and very
obvious this time.

My son was 9 months old.  I believe that little kids have disproportionally
large ears and with this distortion at the top of it, he looked funny.  I
entered the picture in Detroit when the subject was "Humor" and got an
award!

If I was going to shoot 3D portraits today I would use a shorter lens (100
mm) and put the cameras bottom-to-bottom (per Alan Lewis' suggestion) to
get the shortest possible lens separation.  In projection, the audience
sits 2 to 3 times behind the ortho seat anyways so the 100 mm lenses would
bring about the right prespective.

I should point out that the human face is a very familiar picture and such
distortions are very noticeable.  Distortions are all over the place when
we watch stereo projections seated far behind the ortho seat, but it takes
a portrait taken with a Realist to make them apparent!

George Themelis


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