Canon ET-155 (WII) Lens Hood for Select Canon Telephoto Lenses

The ET-155 (WII) Lens Hood for Select Canon Telephoto Lenses from Canon  is a dedicated lens hood for the Canon EF 400mm f/2.8L IS II USM and EF 800mm f/5.6L IS USM lenses.

Lens hoods are primarily designed to prevent unwanted stray light from entering the lens by extending and shading the end of the lens. In addition, since the end of the lens is extended, you get the benefit of extra protection from accidental impact. Dedicated lens hoods are designed to match the specific focal length of the lenses for which they were designed.