If you want ultimate WA quality, and don't mind spending a little...really check out the Nikon 14-24G. You can get adapters for it with focus confirmation, or not. In fact, Lensrentals.com has the 16-9 adapters by Novoflex in stock for rental. This lens blows the pants off of the Sigma, and the 16-35ll....recently took it on a 3 week trip to Italy coupled with my 1D4, and it positively shines. I got mine on Ebay for a measley $1300, but look around. I just took some engagement photos with it this last weekend at the beach...and it rocks. Here is a small example from the engagement shoot...


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and an Italy shot from Siracusa, Sicily, IT at night, hand held with the Mark IV at f2.8 ISO 1600. I have a 20x30 print on metallic paper


from Bay Photo of this and looks awesome!


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