The Pentax 90mm f/2.8 D FA 645 Macro 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. 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.