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[OM] cos^4 explanation

Subject: [OM] cos^4 explanation
From: William Sommerwerck <williams@xxxxxxxxxx>
Date: Mon, 31 Dec 2001 09:32:54 -0800
"I know I'm _supposed_ to know, but why are you 'non grata'?"

Because I'm a loud-mouthed know-it-all sonofabitch who doesn't tolerate stupid
people who don't think, that's why.

By the way, I'm also a PBM -- a QPBM, if you will. Add me (William Sommerwerck)
to the list. And I say that any man who shaves is a traitor to the male gender!

With respect to film flatness -- the faster the lens, the flatter the film
should be, and the more precisely it _must_ be positioned with respect to the
"correct" film plane. This true regardless of the camera type.

With respect to lens mispositioning, SLRs are very tolerant of it, because you
focus through the lens; if it looks right in the viewfinder, it should also be
correct at the film plane (assuming the focusing screen in the same conjugate
position as the film). Viewfinder and rangefinder cameras are less-tolerant,
because you do not focus through the lens. This is why high-quality pocket
cameras were traditionally made of metal. When companies started putting f/2.8
lenses on plastic bodies, the plastic had to be durable enough to hold tight
tolerances for a long period of time, and the body's dimensions had to be
highly repeatable from injection-molding cycle to the next. If such plastics
weren't available, you wouldn't have those tiny XAs and Infinitys to tuck in
your pocket.


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