Canon ET-67 Lens Hood for EF 100mm f/2.8 USM Macro Lens

The Canon ET-67 Lens Hood, as with other lens hoods, is made to keep undesired side lighting from entering the lens.  It does this by extending and shading the end of the lens. Furthermore, since the hood extends from the lens, it gives extra protection from accidental impact.  It is removable and attachable in reverse to take up as little space as possible when storing in camera bag.