The Canon EF 70-300 DO IS USM is Canon's second offering in the DO (diffractive optics) lineup. The 400 mm f/4 was first introduced a few years ago with the promise of longer focal lengths combined with lighter weight. The EF 70 - 300 DO IS USM is the first "affordable" lens from Canon using the new technology.
The 70 - 300 is built very well. Unlike Canon's "L" lenses, the 70 -300 DO carries a green ring designating it's "DO" lineage. The lens comes with a lens hood and carrying pouch. When dialing in a longer focal length, the lens protrudes as focal length increases. Also added is a "zoon ring lock" which prevents accidental extension of the lens. There are two modes for IS (image stabilization), mode 1 for static objects, and mode 2 for panning. All in all, the lens is built extremely well, and carries a lot of features not present on other consumer lenses.