In article
>Can't tell you anything about the Nikon because I bought the Tamron. The
>main reason, of course, is cost; I'm sure you know how much cheaper the
>Tamron is. As for performance, I'll tell you my experience with the
>Tamron. I've tested it at various apertures, and at various focal lengths.
>At 20mm, it is a little bit of a disappointment wide open. The corners are
>*very* soft, and don't improve until f/8, but the softness never really
>goes away completely. It gets better as you zoom in, and is *much* better
>at 40mm. The corners are sharp enough at 40mm that stopping down only
>marginally improves the performance. I on't know whether this corner
>softness is typical of 20mm lenses maybe others can respond. Also, the
>lens is prone to flare, and the hood does a poor job of suppression. I
>have heard that this type of design (wide-angle zoom) is prone to flare,
>so that may not be a problem with just the Tamron. Overall, I am fairly
>happy with the lens. although if I had to do it over again I might go the
>24-50/70 & 20mm prime route, if I were convinced a prime lens would fare
>significantly better.
Um, 20mm Nikkor f2.8's are reasonably good wide-open, though the corners
are soft for my (picky!) taste at f2.8 and f4. By f5.6, performance is
crisp everywhere in the frame (in good samples, which is most of the ones
I've tried - the worst were about a stop behind the best in performance).
The 20mm f2.8 Nikkor is quite free of flare problems. It, and the 16mm f3.5
Nikkor fisheye are my favorite superwides in terms of performance quality
- both produce snappy-sharp images over the whole (wide!) field by f5.6
(which makes hand-holding easy, since DOF is great even at f5.6, and
super-wides can be hand-held successfully at very slow shutter speeds).
Hope This Helps