This is a screw-in type hood that works with lenses at a focal length of 50mm and longer on full frame cameras or 28mm and longer on APS-C sensors. Lens hoods are primarily designed to prevent unwanted stray light from entering the lens by extending and sding the end of the lens. Also, since the end of the lens is extended and the hood features a durable anodized aluminum construction, you also get the added benefit of some extra protection from accidental impact.