Sigma 40mm f/1.4 DG HSM Art OverviewDesigned within the rigorous tolerances of a cine lens, the Nikon F-mount Sigma 40mm f/1.4 DG HSM Art Lens is a wide normal-length lens characterized by a bright design and sophisticated optical layout. The fast f/1.4 maximum aperture helps to achieve shallow depth of field and selective focus effects, and also suits working in difficult lighting conditions. The optical design incorporates a series of low dispersion and aspherical elements, which help to improve sharpness and clarity by controlling both spherical and chromatic aberrations. A Super Multi-Layer Coating is also featured, and helps to minimize flare and ghosting for greater contrast and color accuracy when working in strong lighting conditions.Complementing the imaging capabilities, the lens sports a Hyper Sonic Motor to produce quick, smooth, and quiet autofocus performance with full-time manual focus override. The physical design features a brass bayonet mount, which offers rigidity and mounting precision along with a seal to guard against dust and moisture. Additionally, a rounded nine-blade diaphragm contributes to a pleasing bokeh quality.