The smc Pentax D FA 645 25mm f/4 AL (IF) SDM AW Lens is possibly the most awesome of any Pentax 645 lens--it has the widest perspective of them all, with a focal length equivalent to 19.5mm in 35mm format when mounted on the 645D (15.5mm when mounted on a Pentax 645 film body).
Besides the beautiful visual effects and enhanced depth of field from this ultra wide-angle, this lens provides the highest standards in construction and design. It has two high-performance aspherical optical elements for exceptional images, advanced lens coatings (including Aero Bright Coating for improved performance in backlight situations and SP (Super Protect) coating to repel dust, water and grease), and anti-reflection materials applied to the interior of the lens barrel. The construction is dustproof and weather-resistant for use in demanding environments--this lens is ready, willing and able to leave the studio and go out on location.
A built-in, pull-out filter holder in its barrel makes it easy to use the included circular polarizing filter for improved image control. An advanced SDM (Supersonic Direct-drive Motor) autofocus mechanism guarantees smooth, quiet autofocus operation (manual-focus operation only when the lens is mounted on the PENTAX 645N or PENTAX 645N II camera body), and a rounded 9-blade diaphragm delivers excellent bokeh in the out-of-focus areas in your images. High-quality aluminum machined parts are used for the lens barrel, hood and cap. A Quick-Shift focus system provides instant switching from auto to manual focusing. The lens hood is built-in, and diaphragm control is fully automatic. Awesome.