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.