While this won’t be a straight compare-and-contrast of the 16-35mm vs. the 17-40mm, I think it’s important to note some of the more stand-out differences. Of course, the first thing I noticed was the weight. At 640 grams, it’s slightly heavier than the 17-40’s 470g. It’s not a huge difference, but remember, I’m incredibly used to the 17-40 so it was noticeable. The added heft does give it a good balance on my 5dMKIII with grip, and it was pleasant to use all day during some events I covered. I’ve mentioned in other reviews that 82mm is the new 77mm and with the 16-35 was the first to introduce that filter size in the lineup. I’m not afraid of using circular polarizers on lenses this wide, though you will have to be careful with what type you choose, as any filter that is too thick will definitely cause vignetting at the corners on a full-frame body at 16mm. The rubber focus and zoom rings were smooth and well-proportioned to the size of the body. Mine was a rental unit but didn’t show any signs of being loose. A rubber gasket at the mount makes this lens weather sealed (though a front filter is required to *fully* weather seal the lens). The 16-35 is built to last and work in the most trying of environments.
Canon's rear-focusing Ring USM is excellent - fast, silent and accurate. The Canon EF 16-35mm f/2.8L II USM Lens utilizes the latest auto focus algorithms - though I imagine all new lenses do when they are introduced. I tend to shoot a lot of extra frames when I'm using a new, yet-untrusted lens for shots I care about. Overshooting has proven unnecessary with this lens as I am getting excellent results - accurately focused. The 16-35 L II has FTM (Full Time Manual) focusing enabled. Wide open results are very sharpin the center and improve only slightly stopped down. Wide angle full frame corners, though not perfect, are very good for a lens this wide - the best full-frame Canon wide angle zoom lens yet.