Sigma's 17-35mm f/2.8-4 EX is one of several new EX Series lenses. It combines a fast f/2.8-4 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.