Archived posting to the Leica Users Group, 1998/01/22

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Subject: Re: [Leica] 100/2.8-R macro
Date: Thu, 22 Jan 1998 19:14:34 EST

I have using the 100 mm APO 2.8 for some three years.  At all distances it is
my most favored lens.  I just purchased  a 70-180 APO 2.8 and I just hope it
is a good as the 100mm.

The key word is APO.  This means the lens is corrected to as nearly as
possible using the entire spectrum of light (as least three different points)
for focus.  Prior to fluorite and other special glass chromatic aberation was
corrected using two points and considering the third point.  Now they use
three points.  This is a rudimentary explanation.  The first lens Leica made
was the 180 mm F3.4.  This was developed under a gov't contract I believe.

All the APO lens are tops.  I used the 280 mm F2.8 for awhile but the bulk let
me leave it at home.  I finally sold it.