The Heliopan 39mm Rubber Lens Hood is 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. The Heliopan lens hood is made from real rubber that will not deteriorate from UV rays or from extremes in temperature. The rubber compound is welded on to the black-finished brass-mounting ring so the hood cannot separate from the ring. The hood is convertible from normal to wide angle by rolling it back and it is front threaded for caps and filters. The grooved interior of the shade minimizes flare and helps to direct stray light away from the lens.