P3D PePax challenge # 3

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

This is part #3 of the Trilogy.  Will try and stay out of photo-3d
for a while....

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One way to see this size "anomaly" of a PePax situation is to record a 
portrait with 135 mm lenses and side-by-side SLRs separated by about 
7" (Note:  That's about a 3x increase in both FL and stereo base).  
I took a portrait like that of my 9 month old son and was very happy 
with the results.  I entered it in an SSA folio and Dr. Paul Milligan 
wrote:  "Look carefully at the relative sizes of the nose and ears.  
The ears appear too large or the nose appears too small"  And he went 
on to explain why.

I had not noticed this.  I took a second look and, sure enough, this 
was true!  I was thinking that small children have characteristically
large ears anyway!  But, this picture was almost funny with the big 
ears (and it won an award in Detroit when the subject was "Humor")  I 
looked at a similar portrait of my older daughter (4 at the time) and 
sure enough I could see the "small nose, large ears" phenomenon there 
too.

That's exactly what I said earlier:  In a PePax situation, object that 
are closer appear smaller and/or objects that are further away appear 
larger in size.

A face is a very familiar sight.  Any problems are readily seen.  
I can look at my children close enough when I hug them.   On the other 
hand, I have taken a very nice 135 mm close-up of a bear at the zoo 
and cannot see any deformation there.  Maybe because I never came 
close to hugging a bear?!

How about the Otto Walasek experiment?  Otto used 600 mm lenses and 
the appropriate base to record a picture of a model, looking straight. 
Only the eyes and the nose are in the picture.  There no ears and no 
large distances involved here.  So, it worked and it looked natural 
(especially since I don't know the model personally - I wish! :-) - 
especially the shape of her nose!)

For "deformation sensitive" situations (i.e. very familiar subjects) 
it is recommended that you stay close to ortho.  For example, use 
80-100 mm lenses and bottom-to-bottom SLRs.   If all you have is 135 
mm lenses, still use bottom-to-bottom cameras.  

Another recommendation for portraits:  Don't have the model look right 
into the camera.  With the head tilted to the camera the distance 
between nose and ears is reduced.

That's all I know about PePax.  You are on your own now!

George Themelis


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