The tamron 24 70mm f28 di usd sp lens is a high speed standard zoom super performance sp lens with ultrasonic silent drive usd for fast and quiet autofocus together with full time manual focus override this compact lightweight lens incorporates special high grade glass in three ld elements three glass molded aspherical lenses one hybrid aspherical lens and two extra refractive xr elements to deliver exceptional images along with its moisture resistant construction the tamron 24