Automatic Diaphragm: A lens aperture that stays at it's widest opening until the moment of exposure, when it closes down to the aperture at which it is set. After the exposure, it returns to the widest setting again.
1948: Hasselblad in Sweden offers its first medium-format SLR for commercial sale; Pentax in Japan introduces the automatic diaphragm; Polaroid sells instant black and white film ...
Want the same thing, but with autofocus, instant manual override and an automatic diaphragm? You can't get it from Leica, but you can buy Canon's third-generation 24mm f/1.4, for less than one-third the price, and it works on full-frame digital, too.
"AUTO" signifies automatic diaphragm. The suffix represents the type of lense: "S": Standard, "W"=Wide Angle and "T"=Telephoto. While another example:
U (Uns) for 1 lense element
B (Bini) for 2 elements
T (Tres) for 3 elements ...
Autofocus won't work; the automatic diaphragm, where the lens stays open for focus until the last moment, won't work; and if you have an adapter that doesn't have an optic in it to make up for the change in focus distance of the adapted lens, ...
 See also: Photography, Mount, Focusing, Lenses, Photographer
  
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