OK. I've owned this for about a month. I chose this lens after weeks of deliberation. It eventually came down to the Nikon 12-24mm F4, this Tokina 11-16mm F2.8 or wait for the new Nikon 10-24mm F3.5-4.5. I decided on this the Tokina mainly because of the constant F2.8 aperture. Most independent reviews I have read, rate this lens over the Nikon 12-24 on image quality and on a par for build quality. I have to say I am not disappointed. The corners are a little soft at F2.8 but by F4 the corners are sharp and the Nikons don't go to F2.8. The centre of the frame is razor sharp at any aperture (Certainly from F2.8 to F11).
Filter size is 77mm and with a Hoya HMC UV on the front there is no vignetting I can see at the 11mm setting.
One point to note is that there is no autofocus with this lens on the D40/40X D60 D5000 as it requires a body with a built in AF motor.
Another point of note is that this lens will cover a FX or 35mm frame at the 16mm setting with good to adequate results, so if you still carry a film body along with your DX digital camera you can get away with this lens on both.
Some people may think that the zoom ratio is restricted but most people own an 18mm to something standard zoom so the gap between this lens and that standard lens is tiny. Plus the fact that the zoom range is limited means the designers were able to concentrate on squeezing the maximum image quality from the lens, which they did.
You may have read elsewhere about focus errors on some batches of this lens, I have to say that my example exhibits no errors that I can see, and I am sceptical as to how far out a lens this wide would have to be to exhibit focus errors, as the depth of field is substantial even at F2.8. I suspect that people seeing these errors where actually seeing the slightly soft corners at F2.8 and comparing them with the Nikon 12-24 at F4.
Just to be clear. This lens is sharper than the Nikon 12-24mm at all points of a DX frame at F4.
Oh and SimplyElectronics were excellent and I would use them again.