I'm looking for a wide angle lens to use with my D200. So far I looked at Nikons 12-24mm f4 and Sigmas 10-20mm f4-5.6 and Im tempted to go for the cheaper option and get the Sigma, but the Nikon is also within range if I find thats its worth the extra 400 bucks. But then I found Tamrons 11-18mm f 4.5-5.6 and Tokinas 12-24mm f4. I have no experience with Tamron and Tokina, so are these lense any good? The Tokina seems interesting after reading some online reviews. So any opinions on these lenses?