Re: Converging lenses (was: Window reversal); D|s-TortiO|\|s

[P3D Gregory J. Wageman <gjw@xxxxxxxxxx>]

>Which came first - the company, or the name for the distortion?

>If the latter, it seems strange that the company would have adopted that
>name. On the other hand, there are many common marketing terms for which
>I find it strange that the marketing people decided to use them - such as
>"reduced instruction set computers" and "computer monitor blowout sales". :-)

That would be quite a research project to determine when the term
"keystone distortion" was first used.  But the origins of "keystone"
date back at least to the ancient Romans, who used the classic stone
arch in much of their construction.  The keystone is the specially-shaped
stone at the peak of the arch which distributes and balances the loads
from either side of it:

          -----------
          \         /
           \       /
            \     /
             -----

The "keystone" of the arch is considered of prime ("key") importance
to the arch.  The word has gone on to have a more generalized meaning
of something of particular importance ("the keystone of the plan").
So it's not surprising that a company would name itself "Keystone".
(And Pennsylvania is the "Keystone State".)

The term "keystone distortion" obviously derives from the fact that a
rectangular object assumes this shape on film when the film plane is not
held parallel to the object.  In this case it is a visually descriptive use
rather than a metaphorical one.

	-Greg W.


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