Nice find!
This comparsion also reveals that the Tokina is soft at the extremes wide open, at 50mm more so than 16mm. He also answers a post of which one to choose pointing out that one's shooting preference for wide open vs stopped down and build quality are the crucial factors to consider. My findings as well. In fact I also have a Tamron 17-50mm f/2.8 folder in the same gallery as the Tokina folders ...
http://www.pbase.com/jtsmall/lenses
Maybe of interest to some, buried in the Tamron folder is a brickwall comparson of the Tamron compared to the Nikon 17-55mm f/2.8. I have not had the time to do a brickwall with the Tokina, but it will appear here when available.
Getting back to the factors discussed above, for my style I prefer to stop any lens down 2 from wide open for best sharpness, or f/8 if I'm not overly concerned about isolating the subject. For DOF I tend to limit f/stop to f/11 due to diffraction. However for macros I sometimes close down more. However, if low light or isolation of the subject is critical I shoot wide open. This, of course, argues for the sharpest lens. The rub it that it's at the edge of the frame that the sharpness fails for many including the Tokina -and- the Nikkor. However the build quality of both are vastly superior to the Tamron to my handling.
If however the subject can be kept in the center I don't think it matters which of the three lenses are choosen for most situations. If I'm really concerned about pixel peeping sharpness then I'm pulling out a Macro lens anyway!
Frankly, I would buy the Nikon if it were not 2x the cost of the Tokina ... but then again in many respects the Tokina out performs the Nikon, at least by my interpretation of the photozone.de tests. For me the Tokina wins out, for others the Nikon and for many the Tamron. So, if one chooses with their eyes wide open to the trade offs I think all three are winners.
Again, thanks for posting the link to the head-to-head comparison above.
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-jts
http://www.pbase.com/jtsmall
Canon, Nikon and Olympus
equipment in profile
'From the first moment I handled my lens with a tender ardour.' Julia Margaret Cameron