T3D Convergence as a depth clue

[bercov@xxxxxxxxxxx (John Bercovitz)]

I was aware that if you had to cross your eyes to view a pair, 
the objects in the recreated scene looked smaller than normal 
because the excessive amount of convergence was not ignorable.  
I just did a closeup pair and mounted them in a standard mount 
with the far point set at the normal infinity separation and 
I find that the small objects look somewhat larger than life.  
It appears that viewing with far too little vergence can also 
be a depth clue.  I suppose this is not too surprising but I 
can't recall seeing it so clearly before.

The objects were Chinese snuff bottles from the last century.  
They are small, under 50 mm in their greatest dimension.  The 
distance from camera to objects was under 300 mm and the 
stereobase was 67 mm.  The on-film deviation was well within 
normal (total depth in the scene was kept reasonably low) so 
the pairs are easily and comfortably viewed.  I used the Nikon 
55 mm macro lens and of course it was racked out a ways to 
shoot this close.  I intended the pairs to be projected since 
around 70 mm operating focal length is good for projection.  
However, I viewed them with a 50 mm viewer since that was the 
closest match I had at hand.  So the objects are slightly 
flatter than they should be but it's not by an objectionable 
(easily noticed) amount.

John B


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