This lens hood is a replacement for two Leica S system camera lenses: the 11064 Summarit-S 35mm f/2.5 Asph lens and the 11050 Summarit-S 35mm f/2.5 CS lens. 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 also get the added benefit of some extra protection from accidental impact.