This Sigma APO 50-150mm F2.8 II EX DC HSM is a large-aperture telephoto zoom lens for digital camera use only and is designed especially for portrait photography. Comparable to a 70 to 200mm on a large chip camera, this high quality, professional workhorse is unique as its compact, lightweight body provides freedom of movement and versatility and the large maximum aperture of F2.8 and its shallow depth of field offer greater freedom of creative expression. Most importantly, it incorporates the critical technologies that make it an outstanding optical performer which includes four SLD (Special Low Dispersion) glass elements employed for effective compensation of color aberration and Super Multi-Layer lens coating which reduces flare and ghosting and assures high image quality throughout the entire zoom range. The Internal Focusing System allows for convenient use of a polarizing filter for creative effects & improves the optical performance of the lens at various distances