Archived posting to the Leica Users Group, 1997/12/08

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Subject: [Leica] diffraction limited lens: the theory
From: "Thomas J. Donovan" <75674.3465@compuserve.com>
Date: Mon, 8 Dec 1997 22:58:33 -0500

Erwin Puts,

First & foremost, thanks for posting a highly exegetic MSG; it got me to
thinking about the 280 f4 again. Knowing that Leica themselves has
classified the 280 f4 as a "diffraction limited lens", & taking into
account your MSG; I went to the BAS charts
looking for supporting data.

Sure enough, f8 resolution is ever so slightly lower than f4 resolution; &
conversely f8 contrast is ever so slightly higher than f4 contrast.
Although the differences are slight, it's a pattern that fits your
theories; & L0 & behold, the same pattern applies to the 180 f2.

However, the 180 f3.4 is incredible; both the sharpness & contrast increase
from f3.4 to f8.  Therefore, either the 180 APO Telyt is not a "diffraction
limited lens" or the 
BAS testing is not comprehensive enough. However, maybe it's meaningless to
discuss a lens which is so good that it defies all attempts at
categorization :~)!

If you care to comment; it would be appreciated! In any case these are
truly wondrous "dream" lenses.  Any one fortunate enough to own them
understands what's meant by a "dream" lens ;~)!

Tom D.