Canon's 16-35? Hah. Give it up. Based on my non-scientific testing the Sigma wins. It wins so damn hard. Canon, what are you doing? Sigma is handing you your red ringed ass on a glass platter with their new lenses, and they are doing it at prices that hhobbyists can actually justify. I didn't really have 1,700 for a 16-35. Paying a grand less and getting equal if not better performance? Well, now you have my attention. And probably the wallet.