Canon ET-73 Lens Hood for EF 100mm f/2.8L Macro IS Lens
The Canon ET-73 Lens Hood is designed for the Canon EF 100mm f/2.8L Macro IS Lens. The hood is 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 also get the added benefit of some extra protection from accidental impact. The lens hood will not create any vignetting.