According to "Handbuch des Leica Systems", published
several years, the Summicron 2.0/90 from
2,813,801 to 2,813,900
and
2,997,001 to 3,177,200
has 49mm filter size. Erlier Summicron has 48mm, later 55mm.
The most of them seem to be the first version, according to Laney,
Leica Pocket Book the second version begins with 3,163,007 in
1980.
The serial number of Canada Summicrons may be found on
the barrel.
str.