Nikonos is the brand name of a series of 35mm format cameras specifically designed for underwater photography launched by Nikon in 1963. The early Nikonos cameras were improvements of the Calypso camera, which was an original design by Jacques-Yves Cousteau and Belgian engineer Jean de Wouters. It was produced in France by La Spirotechnique (currently Aqua Lung) until the design was acquired by Nikon to become the Nikonos. The Nikonos system was immensely popular with both amateur and professional underwater photographers. Its compact design, ease of use, and excellent optical quality set the standard for several decades of underwater imaging. Nikon ceased development and manufacture of new Nikonos cameras in 2001, but the camera remains popular, and there is a large and active secondary market. The Nikonos IV-A was introduced 1980 and discontinued is 1984. This camera was part of the second viewfinder line and Nikon's complete re-design included a through-the-lens (TTL) light meter with automatic exposure. The Nikonos IV-A in 1980 and the Nikonos V in 1984 were the second iteration. The IV-A has a Nikon Nikor 2.5 35mm lens, a single action right thumb film advance lever, large viewfinder, shutter release button with locking slide switch, a utility shoe, frame counter, focus knob on the lens assembly with settings of 2.75 feet (0.8m) to infinity, Aperture settings of f2.5 to 22, ASA/ISO settings of 25 to 1600, a fold down rewind crank handle, and a ¼ inch 20 thread tripod socket. The Nikonos IV-A introduced a one-piece body using a hinged back for film loading; sealing was accomplished through numerous O-rings, including a large gasket for the back. The film transport mechanism for the IV-A was adapted from the contemporary Nikon EM. Like the EM, the Nikonos IV-A primarily operated in aperture-priority auto exposure mode using step less quartz-controlled shutter speeds between 1⁄30 of a second and 1⁄1000 of a second, but the camera also offered two mechanical shutter speeds ([B]Bulb and 1⁄90 of a second, marked as M90) in case of battery failure. The Nikonos V retained the new features of the IV-A and added manual control to set discrete shutter speeds. The V was released to address specific criticisms of the IV-A, namely that the flat gasket design was prone to failure, and that the new flash sync shutter speed of 1⁄90 was too fast, especially since slower speeds could not be set manually to use fill-flash.