This is a large aperture lens that provides impressively natural delineation and beautiful shading, as well as excellent performance for indoor photography taking advantage of the bright maximum aperture of f/1.8. The optical system incorporates aspherical lenses, which not only keep the lens size down but also reduce spherical aberration and deliver sharp picture quality. A flare-cut diaphragm installed behind group 1 blocks unwanted light to ensure highest contrast. Operability is enhanced by inclusion of a ring-type USM for silent, high-speed AF with full-time manual focus and a non-rotating filter mount.