1988 Canon EF 70-210mm f/4 Date Code.
UC1204: The C means 1988 and 12 is December.
Canon has been stamping date codes on cameras and lenses since about 1960.
The first letter, "U," means Canon's 3,000 employee, 750,000 sf (75,000 m^2) lens plant in Utsunomiya, Japan, founded in 1977.
"F" would mean Canon's 1,200 employee, 1,300,000 sf (125,000 m^2) Fukushima plant founded in 1970.
"O" will mean Canon's new (production starting May 2007) Oita lens plant with 600 people and 160,000 sf (15,000 m^2), and so on.
Canon uses the second letter for the year. Canon started with A in 1960 and made it to Z by 1985.
In 1986 they started again at A and today, in 2007, have made it back up to V.
The next two digits are the month.
No one has decoded the last two digits.
Early date codes may have had the first letter (the factory code) on the end, so the first letter would be the year.
Canon Year Codes
More Information: Canon's Museum.
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