Sigma AF 17-35mm f/2.8-4.0 EX 

Sigma's 17-35mm f2.8-4 EX is one of the 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.