15mm F/5.6 Auto Nikkor Using an entirely new optical design, Nikon has succeded in producing a lens that provides unprecedented 110 degree picture coverage without the optical distortion associated with ultra-wide angle optics. Furthermore, the 15mm F/5.6 has a back focus 2.45 times greater than its focal length. This means that it permits the automatic miror and diaphragm to function as they do with all Auto-Nikkor lenses. Also, it couples to the camera meter systems. Four filters (Skylight, medium yellow, orange and red) are built into the lens, mounted on a turret with external selector/indicator.