Sigma 17-70mm f/2.8-4 DC Contemporary Macro OS HSM TSC Lens with USB Firmware Lens Dock Kit for Canon and Opteka High Definition HD II UV & CPL Filter Accessory Set Designed to be the ideal all-purpose lens for APS-C sized sensors Equipped with a Hyper Sonic Motor (HSM) and an Optical Stabilizer (OS) for superior image quality. TSC material (Thermally Stable Composite), which allows for increased durability as well a reduction in size by 30% compared to conventional models 16 Elements in 14 Groups; 7 diaphragm blades Two FLD glass elements are incorporated with one SLD element to reduce color aberration