The Nikon F-mount Sigma 18-35mm f/1.8 DC HSM is an Art-series zoom, covering wide-angle to normal focal lengths. Separating itself from the pack, this zoom features an exceedingly bright f/1.8 constant maximum aperture, which suits its use in difficult lighting conditions and offers an impressive depth of field control throughout the zoom range. The optical design incorporates a series of SLD and aspherical elements, which help to achieve high clarity and sharpness by suppressing various aberrations, color fringing, and distortion.  As part of the Art line within Sigma's Global Vision series, this lens is designed to achieve truly notable optical performance and is ideally suited for creative and artistic applications. Impressively bright constant f/1.8 maximum aperture is well-suited for working in low-light conditions and also provides greater control over the focus position when using shallow depth of field techniques. Four aspherical elements are used to help limit distortion and spherical aberrations and also contribute to greater overall sharpness and accurate rendering. Integrated HSM (Hyper Sonic Motor), along with an internal focusing system, realizes quick and quiet autofocus, which is further complemented by an optimized AF algorithm to produce smoother focusing performance. The HSM also permits full-time manual focus control simply by rotating the focus ring at any time. Constructed using a Thermally Stable Composite (TSC) material for greater precision and use in wide temperature variations. Additionally, a brass bayonet affords improved mounting accuracy and rigidity.