The Heliopan 37mm Screw-in Rubber Lens Hood is designed to prevent unwanted stray light from entering a lens by extending and shading its front end. This prevents lens flare and improves image contrast. In addition, since the end of a lens is extended when using a hood, you also get the benefit of extra protection from accidental impact to that lens's front element. This lens hood is constructed with a rubber compound that is UV and temperature resistant, and the rubber material can be rolled back for storage or to convert the hood for use with wide-angle lenses. By rolling back the lens hood, its opening can be made to correspond with a wide-angle lens's angle of view so that vignetting is avoided. A metal mounting ring connects the hood to a lens with 37mm filter threads and a 0.75mm thread pitch. The mounting ring also features corresponding 37mm front filter threads which can be used to accommodate filters, lens caps, or other threaded accessories.