This Pentax HD DA 645 28-45mm f/4.5 ED AW SR Lens  is an ultra-wide-angle zoom lens (incorporating the Pentax-original built-in SR (Shake Reduction mechanism) is designed to optimise the optical performance of the new 645Z, and all Pentax medium-format digital SLR cameras. Providing focal lengths from 22mm to 35.5mm in 35mm format, this is the first lens designed specifically for digital imaging. Thanks to its dustproof, weather-resistant construction, this newest member of the AW (All Weather) series offers outstanding reliability and durability in demanding shooting conditions, allowing photographers to capture images outdoors without worry! For photographers looking to produce exaggerated perspective and expanded depth-of-field shots (unique to wide-angle lenses), this lens is ideal for capturing a range of scenes and subjects; from sweeping landscapes to small indoor spaces. If that wasnât enoughâ¦ its optics consist of 17 elements in 12 groups, including two high-performance aspherical elements and two ED (Extra-low Dispersion) elements, to enhance image resolution and brightness at edges, while minimizing aberrations. Coupled with a high-grade, multi-layer HD Coating** to optimise light transmittance and minimize reflection, and the Pentax-exclusive, high-grade Aero Bright Coatingâ this lens is designed to bring out optimum performance in medium-format digital SLR cameras. * HD stands for High Definition ** A Pentax-original lens coating process developed through the use of nanotechnology. Using a silica aerogel with a uniform porous structure as the base material, this coating produces clear, high-quality images by assuring outstanding anti-reflection performance over a broad wavelength range. Other features include: ã»SP (Super Protect) Coating applied to the front surface of the lens to repel water and grease ã»A rounded diaphragm to produce a smooth, beautiful bokeh (out-of-focus rendition), while minimizing the streaking effect of light ã»Smooth, quiet autofocus operation driven by a built-in DC motor ã»Quick-Shift Focus system for instant switching to manual-focus operation after the subject is captured in focus by the cameraâs AF system ã»Various filters such as the C-PL (circular polarizing) filter can be attached to the front of the lens – a unique feature for a wide-angle lens.