I've had this lens now for 5 years. It's a very interesting lens as it is designed for crop sensor cameras, but as many have noted, it works on full frame cameras from approximately 14-16mm, and works on APS-H cameras from approximately 12-16mm. When first bought this lens, I was still shooting crop sensor cameras, and as many know, this was the go to ultra wide angle lens for crop sensor cameras if you needed a fast aperture. I of course fell in love with it, and was very excited to see that it still "worked" on full frame cameras when I made the switch a couple of years back. Some people might ask themselves, how useful is a lens that covers such a small range natively, and an even smaller range on a full frame camera. I treat it like a prime lens that has a little bit of flexibility.
A relatively small front element compared to the 77mm filter thread. Notice the short throw on the zoom ring, as well as the large amount of reflections in the elements. The newer version corrects this with better coatings, reducing flare. (And yes, those are Terry Pratchett Discworld novels in the background!)
The build quality of this lens is phenomenal, especially for a third party manufacture. During that time, most other 3rd party lenses like Tamron, and Sigma were not build up to level of higher end Canon and Nikon lenses. Tokina was the main exception. The lens barrel is metal, metal internals, metal mount. The only thing that isn't metal (besides the glass) is the filter ring, and the focus ring. End result, this lens feels like a tank. More so than some of the Canon L lenses. Unfortunately, this lens is not weather-sealed.
Auto focus is done internally by a DC motor. It is surprisingly quiet and fast though. A slight buzz can be heard as it focuses, but being such a wide angle lens, it doesn't have that far to go in order to achieve focus. This lens does not have manual focus override, but features a clutch system for switching between auto and manual focus. Simply pull the focus ring back towards the camera until it clicks, and manual focus has been engaged. To switch back to auto focus, simply push the ring forward away from the camera, and it will click back to auto focus. The zoom ring is incredibly well dampened, even though it is a short throw of the ring. It doesn't take much time to get from 11mm to 16mm. While the numbers may seem close, the distance is quite significant due to how wide the field of view is.
Optically, this lens is quite good. Good resolution and sharpness throughout the entire range wide open, and it just gets better when stopped down. Vignetting on a crop sensor camera is pretty well controlled towards the 16mm end, and gets a little worse towards 11mm, but it is still manageable. On a full frame, it's worse, but keep in mind it is not designed to work on full frame. Wider than 14mm on full frame, and you begin to start to see the back of the lens. There are 2 big downsides to the lens. Chromatic aberration can be a little rough sometimes, but generally can be removed in post. The bigger issue is flare. It is a complex design with a lot of elements. Combine that with it's field of view, it makes this lens quite prone to flare. Fortunately if you are aware of how this lens flares, most of the time you can change the framing slightly and remove most of the flare issues.
One of the great things about ultra wide angle lenses is the ability to emphasize the distance and size of objects, and add extra drama to a shot. I love shooting overhead of crowds or dance floors with this lens because of the energy and drama that it puts into a shot.
Overall, I really like this lens. It's great that it "works" on both crop cameras and full frame cameras. It means you don't have to worry about selling it if you switch to full frame. (Obviously you can, but not necessary) Compared to the price of a Canon 14mm f/2.8L II, it's certainly a nice option for having a 14mm on full frame. Another option is the popular Samyang 14mm f/2.8, which is cheaper, but lacks AF, and has a much more complex distortion. The corner sharpness does not appear to be as good in some copies. I've gotten a lot of shots with this lens that wouldn't have been able to get had I only had a 16-35mm on me. The difference between 16mm and 14mm is quite significant.
To view other photos from this lens and view photos in high resolution, head over to my Flickr page where I have the photos posted in full resolution, and check out the results for your self!