The Sigma 17-70mm offers a relatively long zoom range 4x ratio coupled with an impressive large maximum aperture at 17mm. The 17-70mm DC Macro is specifically designed for the reduced image circle of today's APS-C DSLRs where the field of view is equal to 26-150mm (full format). It incorporates inner focusing system, which ensures fast AF speed, as well as, prevents the front of the lens rotating. SLD and two aspherical glass elements help eliminate chromatic aberrations while providing superb image quality throughout the zoom range. Super Multi Coating on the glass minimizes flare and ghosting and ensures high contrast images.