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.