Genus adaptor rings come in a range of sizes to suit most cameras & lens. Not all lenses are made to the same diameter, therefore a lens adaptor ring is required to attach your lens to a matte box. Made from high grade aluminium, Genus lens adaptor rings are precision crafted to ensure that each one will screw on to your lens smoothly. Angled grooves on the outer circumference make sure that your adaptor ring will slot snugly & securely into the donut ring