The 16-35mm f/2.8L USM is a wonderful lens. I have used mine on my 10D numerous times with great results. I would keep an eye out for the 17-40mm f/4L USM though. The optical performance appears o be better at 17mm than its faster brother. Unless you really need the speed and extra 1mm then I would go for the 17-40. Only $800 compared to $1360 for the faster zoom.