P3D Re: formats and focal lengths

[Bruce Springsteen <bsspringsteen@xxxxxxxxx>]

Brian and George gave wonderful explanations of perspective - but it
drives home to me how hindered we are, using email to discuss visual and
geometric topics.  The hundreds of words we spend trying to clarify this
stuff on P3D could often be avoided in a few of face-to-face
conversations, drawing on a cocktail napkin.  Alas.

As regards stereo, the important points about perspective, to me - and
hopefully responding to Mr Goodman's self-described "newbie" confusion -
are as follows:

Squash and stretch have *nothing* to do with stereo base.  Zero.  Nada. 
The notion that hyperstereo stretches an image is a common misperception
of the scaling effects of base changes.  Many people will try to tell you
otherwise.  It is a fallacy. 

Indeed, squash and stretch are not characteristics peculiar to stereo at
all.  They are characteristic of any photography, or any perspective
projection, photographic or drawn, when the apparent viewing position is
effectively different from the true drawing or shooting position, as
George explained so well.

The phenomenon unique to stereo is not perspective, but parallax.  The
effect of changes in base is solely to change the apparent size and
distance of the scene - miniaturization or enlargement.  But the mind can
be confused about which effect it is seeing, especially without practice
observing, and the effect of hyperstereo is often confused with stretch.
 
Bruce






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