The Pentax HD D FA 645 Macro 90mm F2.8 ED AW SR Lens  is a fast, medium-length lens (equivalent to 71mm in 35mm-format) for use with Pentax 645-mount medium format cameras. Compatible with Pentax 645 AF2 lens mounts.The f/2.8 maximum aperture provides greater control over depth of field and features rounded 9-blade diaphragm construction. This lens has the Pentax Quick-Shift Focus System for rapid switching between auto and manual focus modes, and integrates a Shake Reduction mechanism for countering the effects of camera shake or image blur.Both an HD Coating and Aero Bright Coating are applied to lens elements in order to improve overall light transmission while reducing flare and ghosting. A Super Protect (SP) coating is also applied for protection against the elements and to ease cleaning of the lens. In addition to the SP coating, the overall construction of the lens is also weather resistant and dustproof.Medium portrait-length lens is equivalent to 71mm in 35mm format, giving a slightly longer-than-normal angle of view.Fast, bright f/2.8 maximum aperture helps control depth of field and enables greater versatility when working in low-light conditions.Quick-Shift Focus System allows you to instantly switch between auto and manual focusing modes.HD, Aero Bright, and SP coatings help to improve light transmission, reduce lens flare and ghosting, and aid in greater protection for the lens surfaces.Dustproof and weather-resistant construction provide increased protection when working in poor conditions.