Canon EF 100mm f/2.8 Macro USM Fixed Lens for Canon SLR Cameras International Version (No Warranty) 100mm macro USM lens with f/2.8 maximum aperture for Canon SLR cameras Secondary diaphragm blocks stray light at f/2.8 for increased contrast Ultra-sonic monitor provides outstanding autofocusing speed at all distances 3-group floating system for exceptional close-up performance; full-time manual focus Measures 3.1 inches in diameter and 4.7 inches long; weighs 21.1 ounces