Re: focal lengths

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

>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)?  >Ray Hannisian

I am sure that John B. will give a more accurate explanation of this but
here is how I see it:   By increasing the distance between the lenses
you are trying to simulate the extra depth seen if you were positioned 
closer to the subject, but since you actually have not gone closer to the 
subject, the prespective is all screwed up.

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.  But because I stayed far away, I
created this "distortion".  Paul Milligan suggested that I use shorter
lenses (85 mm).  This will bring me closer to the subject.  

This perspective distortion is there in both 2D and 3D.  The viewing
conditions are important too (I was using the red button's 45 mm FL lenses,
too short compared to the 135 mm taking lenses).

George Themelis


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