P3D Re: Keystone

[fj834@xxxxxxxxxxxxxxxxxxxxx (Dr. George A. Themelis)]

>I think the warnings about keystone distortion with toed-in cameras have
>missed a significant point.  The original question involved a stereo base
>of about 30 feet.  Assuming the ol' 1 in 30 rule, for the sake of
>argument, that puts the closest object 900 feet away.  The perspective
>distortion at that distance will be zero to as many decimal places as you
>like, surely?

Hmmm, not really.  Ever heard of "similar triangles" :-)  It does not
really matter if your subject is 900 or 9 feet away.  If you double the
distance (from 900 to 1800 or from 9 to 18) sizes are cut in half.  
It is a matter of ratios.  If you draw a figure to explain keystone
the figure has no scale.  The only point you can argue is that if
you maintain the 1:30 ratio then keystone distortion "mismatch" would 
should not be a problem.

George Themelis


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