Introduced in 1975, the Olympus OM-2 was a semi-automatic, aperture-priority camera featuring an electronically controlled shutter. It was based on the OM-1 body, and retained compatibility with OM-1 accessories and lenses. It boasted automatic through-the-lens (TTL) off-the-film (OTF) metering, and exposure was considered very accurate. This was calculated by the measured light reflected off the surface of the shutter, and/or the film surface during the actual exposure. The camera also offered a manual-exposure mode, as in the OM-1. It also introduced the integration of electronic flash into the exposure system using the TTL exposure system. OM-3 The OM-3 was an updated version of the OM-1, a manual camera without automatic exposure modes, and an entirely mechanical shutter. It featured a multi-spot metering system (shared with the OM-4) in addition to the centre-weighted metering of the earlier body. It also featured an LCD similar to the OM-4 which could be illuminated in low light. Its main advantage over the OM-4 was its ability to operate without batteries due to its mechanical design. Batteries were only needed for the exposure meter and LCD. It lacked a self-timer and mirror lock-up functions, however. In 1995, nine years after the OM-3 was discontinued, the OM-3Ti was released. It shared the improvements over the OM-3 that the OM-4Ti held over the OM-4. OM-4 The Olympus OM-4, an improved version of the OM-2, was manufactured from 1983 to 1987. It was introduced at a US$685 list price for the body alone. It was a battery-powered, electromechanically controlled, manual focus SLR with manual exposure control or aperture priority autoexposure. It used a horizontal cloth focal plane shutter with a speed range of 240s (in auto mode) to 1/2000s plus bulb, and flash X-sync of 1/60s. The OM-4 featured a built-in spot meter [of a narrow acceptance angle, see Canon FTb] (2% of view; 3.3˚ with 50 mm lens) and was the first camera capable of measuring eight individual areas and averaging them. The light meter used a dual-concentric segmented silicon photo-diode to provide spot or centerweighted readings. It used a graduated linear LCD for the shutter speed at the bottom of the viewfinder to precisely indicate its readings versus the actual camera settings. In 1986 the OM-4 was improved to a tougher OM-4Ti (OM-4T in USA) version, with titanium top and bottom plates, improved weatherproofing and high-speed flash sync. This last version was discontinued in 2002. Consumer-grade