Sigma's 17-35mm F2.8-4 EX is one of three EX Series lenses. It combines a fast F2.8-4 maximum aperture with ultra wide angle zoom lens of 17-35mm. It incorporates aspherical lens elements in the front, as well as rear lens groups, to correct spherical aberration. It also incorporates internal focusing to prevent deterioration of the optical quality at close distances and to eliminate rotation of the front barrel during focusing. A "perfect hood" is provided. The AF drive for Sigma SA and Canon SLR cameras is equipped with a silent, responsive and fast Micro Hyper Sonic Motor. The lens materials used in this new lens are lead and arsenic free ecological glass.