P3D Keystone

[David Spacey <spacey@xxxxxxxxxxxxx>]

Hi All,

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?

On the subject of real keystones, Brian Reynolds wrote:-

>The keystone of an arch is the center stone against which both halves of
>the arch press.

It's a common misconception that there is anything special about the
central stone of an arch.  In engineering terms the keystone is no
different to the others.  It takes precisely the same stress, in the same
directions relative to the stone's orientation.  People tend to over-rate
the centre stone, and make it bigger and decorated etc., because it's the
last to go in.  Before you have something that will fall down under it's
own weight.  After it will hold many times it's own weight.  Magic!

Dave Spacey
____________________________________________________________________________

Walk tall, walk straight,
Spit the world right in the eye.

-Kevin Godley and Lol Creme


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