This lens is part of Sigma's Art line; deeming it well-suited to creative image making due to its large, constant f/1.8 maximum aperture and ability to produce aesthetic bokeh by way of a nine-blade circular diaphragm One aspherical lens element, as well as the incorporation of SLD glass, help to minimize the appearance of distortions and aberrations throughout the zoom range and provide clear imagery with enhanced sharpness The Hyper Sonic Motor provides fast, quiet and smooth auto focusing that is well-suited for use with video applications. This AF motor can also be manually overridden at any time by rotating the focusing ring, giving you the ability to fine-tune Constructed using a TSC compound material, this lens is lightweight while also exhibiting notable durability and resistance to environmental changes