The Pentax 28-45mm f4.5 ED AW SR HD DA lens with 645 mount is an ultra-wide-angle lens with SR Shake Reduction for use with the 645D and 645Z medium-format DSLR cameras. This weather-resistant lens provides a 35mm equivalent focal length of 22-35.5mm, making it great for capturing a wide variety of scenes and subjects, in particular images with an exaggerated perspective. Its optics consists of 17 elements in 12 groups, including two high-performance aspherical elements and two extra-low dispersion elements. In addition, the Pentax-innovated SR mechanism has been incorporated into this versatile lens, which effectively compensates for camera shake up to approximately 3.5 shutter stops.