Canon EW-83E Lens Hood for the Canon EF 16-35mm f/2.8 L USM, EF 17-40mm f/4L USM, EF-S 10-22mm f/3.5-4.5 USM lenses

Canon lens hoods are made specially to stop light spilling into the lens and wrecking the photo. Lens hoods are also great protection should you drop the lens on its nose.