The dedicated Canon EW-73E Lens Hood is specifically designed for use with the Canon RF 15-30mm  and RF 16-28mm lenses. It is primarily used to prevent unwanted stray light from entering the lens by extending and shading the end of it. This hood features a non-glare finish on the interior surface to further prevent or limit lens flare. Also, since the end of the lens is extended, you get the added benefit of some extra protection from accidental impact.