Ken Rockwell schreibt beim 18mm f/2.8 AF-D:
If you want similar optical performance for less money, try the 20mm f/2.8 AF. The 20/2.8 has better ghost performance and the same sharpness and distortion performance as this far more expensive 18/2.8D AF. I still prefer this tougher 18mm for its wider view and standard 77mm filter size.
An anderer Stelle (17mm und 18mm Schärfevergleich):
The Nikon 18mm f/2.8 AF-D also looks bad here, but just happens to be half the size and weight of either zoom, is built as pro-tough as the Nikon 17-35mm f/2.8 AF-S, and is also unbeaten in speed. It is uncommon, and a great lens for a pro traveling light.
Hier bemängelt er noch die starke Vignette und dass die Ecken nie scharf werden. Da gefällt ihm das Tokina AT-X 17mm f/3.5 AF besser.
Beim 20mm f/2.8 AF schliesslich:
I used to use this AF 20mm all the time because it's small and easy to use. I'd rather tote it around instead of the fat $1,500 17-35mm AF-S. This lens is not quite as sharp as my old 20mm f/4 AI manual focus. It's not quite as good as the 17-35mm F/2.8 AF-S zoom, which may be a first zoom to be a tad sharper than a fixed lens. The zoom also has less light falloff at f/2.8. How about that!
Ich werde da nicht so recht schlau draus. Auch stelle ich mir die Frage, wieviel das Tokina RMC II 17 mm f/3.5 mit dem Tokina AT-X 17mm f/3.5 AF zu tun hat.