[OM] 28mm

[Machiel]

I am (also) looking into the Zuiko 28mm f2.0 and have some questions.

-    this lens has a close-distance correction mechanism - what does that mean?
-    I read this did not exist in the earliest version - is there a way of 
telling which version is which (lens nrs?)
-    Anyone has experience with this and can tell something about the practical 
difference between yes/no close distance            correction mechanism?

Thanks, Machiel