Nikonos IV-A, an electronically controlled 35 mm focal-plane shutter type underwater camera, was introduced in 1980. Owing to its robust construction, it needs no additional housing for depths to 160 feet (50m). It can take interchangeable lenses. The most popular lens is the 35mm f/2.5 which may be used on land, sea, or air making it fit for use in dirty, dusty and wet environments. It is primarily operated in aperture-priority auto exposure mode using step-less quartz-controlled shutter speeds between 1/30 and 1/1000 but the camera also offers two mechanical shutter speeds ([B]bulb and 1/90, marked as M90) in case of battery failure. Lens: Nikkor 35mm f/2.5. Lens mount; NIKONOS mount.