Thanks dr Croubie, that was helpful! (Paint scratches OK, look out for dents and dings.) One of the sellers states that he is selling because the lens has only been used a handful of times. How genuine could that be? Who would only use THAT lens a handful times and then sell it? :-) I'm OK with an off calibration since my 5D mkII lets me adjust calibration for every lens.

I thought I knew what a "dog" was, but now I am not sure. What is a "dog" lens?

Hilde