Review: "The 12-24/4 is Tokina's offering in the popular "superwide zoom" category for APS-C format digital cameras. In this category it competes with the Sigma 10-22, Tamron 11-18 and Canon 10-22. None of these lenses has full frame 35mm coverage and so all are specified for use only on cameras with APS-C sized sensors.
In terms of optical quality the Canon may be a little sharper in the corners wide open at the wide end and the Tokina may be a little sharper in the corners wide open at the long end, but overall the optical quality of the two lenses is pretty similar. If forced to say which is the overall sharper lens, on the basis of pixel peeping at resolution test chart images I'd have to give the edge to the Canon 10-22 - but based on real world shots it would be pretty hard to tell...."
Joby Gorillapod Focus
