Designed to prevent stray light from entering the lens in order to keep unwanted glare from affecting your photographs.
Canon lens hoods are one of the most important accessories for each lens you own. A lens hood provides multiple functions: it shades the lens from stray light, improving your contrast and image quality in inclement weather, it can assist in keeping moisture or wind-blown debris off the lens and it protects the front barrel from the inevitable impacts against walls, door frames, and other real-life obstacles. Almost all EF and TS-E lenses have a Canon lens hood engineered specifically for it. For Canon EF 16-35mm f/2.8 Lens
Compatibility
EF 16-35mm f/2.8L II USM