The EF 100mm f/2.8 Macro USM from Canon mixes a comfortable short telephoto focal length with a short working distance. A three-group internal floating focusing system is also used to maintain image quality throughout the entire focus range and Ultrasonic Motor provides quick and quiet autofocus performance, along with full-time manual focus control. Short telephoto prime is designed for full-frame Canon EF-mount DSLRs, however, it can also be used with APS-C models where it provides a 160mm equivalent focal length. One ultra-low dispersion (UD) element greatly reduces chromatic aberrations and color fringing for improved clarity and color accuracy. A ring-type Ultrasonic Motor (USM) is employed to deliver fast, precise, and quiet autofocus performance as well as full-time manual focus override. Focus Limiter switch lets you constrain the focusing to two different ranges for faster focusing performance: 1′-infinity and 1.6′-infinity.