This dedicated ZEISS Lens Hood is specifically designed for use with the Distagon T* 18mm f/4 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 is extended, you also get the added benefit of some extra protection from accidental impact. The hood is included with the 18mm f/4 and is offered here as a spare or replacement part.