Archived posting to the Leica Users Group, 1997/02/19

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Subject: F-Stop Calculations
From: photology@juno.com (Thomas P Myro)
Date: Wed, 19 Feb 1997 19:30:58 EST

Good Day!

Since PJW took all that time to measure 12 of his lenses-- I figured I
would take the time to do calculations in order to prove hime wrong.

What actually happened is that I proved him RIGHT.  Our system of
numerical apertures IS calculated by dividing the focal length by the
physical aperture.

I still think that measuring the diaphragm by the way it looks is just a
coincidence-- otherwise all those lens designers using apertometers all
of these years will commit suicide when they find out all they really
needed was a good starrett.  Hey-- If all you need to do is measure by
the apparent opening in the diaphragm I could put a Proxar close-up lens
on my 50f1.5 Sonnar and I'll have a f1.1 for my Contax -heh heh heh .

Honestly, Peter, you have my apologies, I was wrong-- beat me flog me
kill me dead.

Dr. Abbe's aperture system of calculating numerical aperture must be an
antuquated system -- I've rechecked what the catalogues said, and I did
interpret it correctly, although I was always told that we used HIS
system today.

Oh well, this won't be the last time I'll be wrong.

Sincerely,

Thomas P. Myro
Photology@juno.com