Summary: If you're considering it for Canon, give me a week and I ought to have a read on it versus the Canon ultrawide zooms. I am expecting that this Tokina will be optically superior to any Canon ultrawide zoom, L or otherwise.
Excerpt: The first lens in a promised line of AT-X Pro FX full-frame Tokinas, this is also the company’s first with a highly refined, micro AF motor that’s both silent and fast-focusing. Approximately a 26–45mm equivalent on Canon’s APS-C bodies and 24–42mm on Nikon’s-—the only mounts in which it’s available—this $850 (street) lens zooms and focuses internally for a completely stationary barrel.
Excerpt: The Tokina 16-28mm f/2.8 AT-X Pro FX Lens is an affordable, ultra wide angle lens with an also-ultra wide f/2.8 aperture available over the entire focal length range. That this lens is full-frame-compatible adds greatly to its desirability. This is a solidly-built lens with a heft, thanks to the large amount of glass required by this design.
Excerpt: Much bigger than most lenses, and at more than twice the weight of some, the Tokina AT-X 16-28mm f/2.8 PRO FX is a chunky lens. That's because while other lenses are designed solely for use on cameras with APS-C or Four Thirds sensors, the Tokina is fully compatible with full-frame cameras.
Tokina AF 16-28mm f/2.8 AT-X Pro SD FX (EOS) - Full Format Review / Lab Test Report
21 February 2012
Conclusion: The Tokina AF 16-28mm f/2.8 AT-X Pro SD FX is a high-performance ultra-wide zoom lens that gives the Canon EF 16-35mm f/2.8 USM L II a run for the money - but it's not a lens without flaws. Its primary weakness is corner softness at f/2.8 but that's not unheard of in this class anyway. However, the center quality is great and the borders are generally sharp as well. The corners start to catch up at f/4 and they're very good from f/5.6 onward.
Pros: You want a fast ultra-wide angle zoom lens for a reasonable price., You require superior performance and build quality. Don't buy this lens if :, You use a DSLR with an APS-C sized sensor., You want to use filters., You require a lightweight lens., You want to shoot close-ups.
Excerpt: The Tokina AT-X 16-28mm F2.8 Pro FX lens has a rather noisy auto-focusing system, with an easily audible mechanical whirr. In use, we found the system satisfyingly quick and accurate on the Canon EOS 5D Mark II, with no complaints about speed or accuracy.