The HB-65 Bayonet Lens Hood from Nikon is a black petal-style lens hood designed for the AF-S NIKKOR 80-400mm f/4.5-5G ED VR lens.
Lens hoods are primarily intended to prevent unwanted stray light from entering the lens and causing flare. They also provide a degree of protection for the lens from accidental impact and from the elements.
The "petal" shape of this snap-on lens hood maximizes the amount of hood coverage for the minimum amount of weight and hood area. This dedicated lens hood is designed to match the specific focal length of its lens, deflecting stray light without extending into the frame.