When it comes to optical quality, the Tokina also has good and bad points. The most obvious downside is a small amount of vignetting, even with the small sensor Canon EOS 20D. This is quite noticeable at f2.8 but has gone by f5.6. In practical day to day use I haven’t found this a problem, but it is there. I’m planning to test the lens with a Canon EOS 5D soon, and will update the test then. Chances are vignetting will be a bigger problem with the Canon 5D or 1Ds. Sharpness is good at full aperture - not as crisp as my Nikon 300mm f2.8 but there isn’t a huge difference, and by the time you reach f5.6 I’d say the Tokina is actually a little sharper. Comparing shots taken on different camera bodies is a little unfair, so the best comment is perhaps just to say that both are very, very sharp.
In the field, both autofocus speed and accuracy have been excellent - just so long as I remember not to hold it by the focus ring. I’d say my hit rate for pin sharp pictures with this lens is at least as good as with my Nikon 300 2.8. Of course, that’s shooting static subjects from a slow moving camera position - usually a helicopter. I suspect sports photographers probably do need a Nikon or Canon lens, and would have to rule this lens out on autofocus performance alone.
<< That focussing ring - As the manual focus ring moves during autofocusing, you have to remember to keep your hands clear and hold the lens by the serated ring on the front section of the lens