The Sigma 18-35mm f/1.8 DC HSM Lens for Canon is a wide-angle to normal-length zoom lens that features a fast, bright constant f/1.8 maximum aperture. It is specifically designed for use with APS-C-sized sensors and provides a 35mm-equivalent focal length range of 28.8-56mm.The lens integrates one aspherical element into its construction as well as Special Low Dispersion (SLD) glass to help minimize various aberrations and distortions throughout the zoom range as well as provide greater image sharpness and clarity. A Super Multi-Layer Coating has also been applied to lens elements to reduce surface reflections, lens flare and ghosting to produce images with higher contrast and color fidelity. The lens barrel design is constructed from a Thermally Stable Composite (TSC) material that is akin to metal in texture and resistance to temperature and environmental changes while also remaining lightweight and compact. An internal focusing and zooming mechanism also helps to maintain a compact and consistent overall length and non-rotating front ring also better enables the use of circular polarizing filters. For control of focus, a Hyper Sonic Motor (HSM) is used to ensure fast, precise and quiet focusing capabilities that are well suited to continuous shooting and movie recording.For updating lens firmware and fine-tuning its nuances to best suit your personal shooting, this lens is compatible with the Sigma USB Dock. The dock allows you to specify certain parameters