Like the Canon 70-200 f/4, this is a less expensive “L” quality lens that has very good image quality. I prefer it to the Canon 16-35 f/2.8 for landscape and outdoor wide angle shots. It’s every bit as sharp, perhaps sharper, and more flare resistant. Plus it takes more reasonably priced 77mm filters. If you don’t need f/2.8, this is the wide angle lens of choice for full frame cameras in my opinion.

On a crop frame camera, the Canon 17-55 f/2.8 IS offers image quality nearly as good with added image stabilization. It’s a bit more “fragile” than the 17-40, though.
March, 2013