Canon ET-65III Lens Hood Compatible with EF 85mm f/1.8, 100mm f/2.0, 135mm f/2.8 SF & 100-300mm f/4.5-5.6 Lenses - Durable Sun Shade for Outdoor Photography, Portraits, and Travel Shots

The Canon ET-65III 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.