Re: Portraits in Stereo

[P3D John Bercovitz <bercov@xxxxxxxxxxx>]

Errors in perspective of photos taken of nearby familiar objects 
are readily detected by the human visual system.  Although these 
errors are more readily detected in stereo, they're also easy to 
spot in monos.  The classic error is that of taking a full frame 
mono portrait with a very short lens.  A person can't get close 
enough to the resulting photo to view it properly (because it will 
be too close and therefore out of focus) unless the photo is blown 
up to mural size and viewed up close.  So when perspective is 
critical, such as in portrait work, we make an attempt at using 
the correct focal length camera lens for the viewing conditions 
that will follow.  What is most critical is the human face if it 
is a well-known face.  We can easily calculate the correct camera 
lens to use.  As an example, suppose we are going to have 4x6 
prints made.  Usually we will view these from about 16".  A 4x6 
print is ~a 4X enlargement.  16"/4X = 4" so we should use a 4" or 
100 mm lens to shoot when perspective is critical and viewing 
conditions are as stated.

John B


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