The high performance DA* 300mm ED (IF) lens incorporates an SDM system which creates a smoother, quieter auto focus. Featuring a Quick-shift Focus System, switching from auto focus to manual is instantaneous. Weather and dust resistant, it's the perfect lens for extreme weather conditions. Developed specifically for PENTAX digital SLRs, the DA* 300mm ED (IF) SDM lens has PENTAX SP coating which protects the exposed lens elements, and a focal length equivalent to 450mm in the 35mm format. The Pentax 300mm F/4 is commonly used for Landscape/scenery, Sports/action, Wildlife photos and more.The Pentax 300mm F/4 is most used by customers who consider themselves to be a Photo enthusiast among others.The Pentax 300mm F/4 is popular because customers like the following qualities of the Pentax 300mm F/4: Consistent output, Durable, Easily interchangeable, Fast / accurate auto-focus, Nice bokeh, Rugged and Strong construction.