I'm looking into buying a new lens and I know what I want...a wide-angle zoom lens. Before I go about spending the money on this lens (it being an L series, its not exactly cheap) I need some help. I've seen both the EF 16-35mm f/2.8L USM and the EF 16-35mm f/2.8L II USM being sold used. What I would like to know is if there is really any great difference between the two, how much of a difference, if anyone has one (or both) and if the II is really worth the extra money (buying used). Thanks.