The Sigma 18-35mm f/1.8 Art DC HSM Zoom Lens is the first wide-angle to standard zoom lens to achieve a large aperture of f/1.8. Designed specifically for APS-C sized sensors it translates to 27mm-52.5mm on 35mm camera. It incorporates a wide glass molded aspherical lens with Special Low Dispersion (SLD) glass. Internal focusing and zooming. Additional features: Hyper Sonic Motor (HSM) Thermally Composite Material (TSC) Global Vision design 9 blade rounded diaphragm plus more!