This distinctive green-ringed lens is one of only two which Canon make to incorporate their unique Diffractive Optics technology. We don't understand the physics very well, but the basic upshot is that it allows lenses to be much smaller than would otherwise be the case. Some reviewers have suggested that the optical performance is not on a par with conventional lenses, but if you don't mind doing a bit of post-processing to increase the contrast then this lens will deliver great results.

The build quality of this lens is very high and it is designed to make a very good travel lens. Because, as we all know, a lens that is easy to carry around will get MUCH nicer shots than a lens which is left at home because of its size/weight!