Pentax Fixed 55mm f/2.8 Standard Lens for Pentax 645D Fixed 55mm f/2.8 lens designed for the Pentax 645D Fully weather sealed design to work with the weather sealed 645D. Quiet SDM autofocus motro provides fsta and accurate autofocus operation. Curved aperture blades provide a circular aperture at f5.6 for extremely smooth image bokeh. Pentaxt quick shift autofocus instantly shifts from auto to manual focus for on the fly focus accuracy.