Quote Originally Posted by John Koehrer View Post
Leica.overgaard.dk seems to disagree with your definition. Summicron was derived from Leicas use of crown glass for the first time.
ALL Summicrons are f2 maximum aperture.
-M says it's an M mount lens not an R or reflex lens

Not all Summicrons have finger tabs, in fact MOST do not.
I think you're getting mixed up here.

The Summicron was the first Leitz lens to use LANTHANUM crown glass. Normal crown glass has been in regular use in optics since the 1730s; without it, there would have been no achromats until the 1950s.
"Summicron" is a progression of the Summar/Summitar/Summarit naming convention for double-Gauss normals. If you can get -cron out of "lanthanum", I salute you. :P

f/2 is the middle speed of Leica's lineup, between 2.8/2.5 and 1.4/1.0/0.95. All 'Crons are f/2, and all 'Crons are also mid-speed.

Most M-mount lenses don't have -M in their names. That's a recent convention. A Summicron 50 f/2 and a SUMMICRON-M 50 f/2 are not the same lens, either optically or mechanically.