The Pentax-D FA 645 55mm f/2.8 AL [IF] SDM AW Lens is the first model of the Pentax-D FA 645 lens series created for the Pentax 645D digital medium-format camera. With a focal length that's equivalent to a 43.5mm standard lens (in 35mm), it features optics optimized for digital photography to assure exceptional performance, and also provides an image circle covering the image area of existing 645-format film SLR cameras. It has dependable, dust-proof, weather-resistant construction for active outdoor photography. This lens features a Supersonic Direct-drive Motor (SDM) autofocus drive and Quick-Shift for instant autofocus/manual focus switching, Aero Bright coating to help prevent flare and ghost images, and it's Pentax's first 645 system lens to incorporate a rounded diaphragm for improved bokeh (the aesthetic quality of the blur in the out-of-focus areas of an image). FEATURES: Fixed 55mm standard-length focal length lens.Pentax 645 AF2 bayonet mount can be used on older PENTAX film 645 bodies.Advanced optical design, including lens curvature and optical coatings, is optimized for the exacting needs of digital photographic sensors.Quiet SDM autofocus motor provides fast and accurate autofocus operation.Fully weather-sealed design works with the 645D weather-sealed body for maximum reliability in the field.Fast F2.8 maximum aperture allows outstanding depth of field control, while maximizing shutter speeds for existing light photography.Curved aperture blades provide a circular aperture at F5.6 for extremely smooth image bokeh.Pentax Quick-Shift autofocus system instantly shifts from auto to manual focus for on-the-fly focus accuracy.