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Definition: Four Thirds system

A standard for digital single lens reflex (DSLR) cameras from Olympus and Kodak. It uses a large CCD with a 4:3 aspect ratio and a lens mount opening twice the size of the CCD image circle. Because CCD sensors are set in slightly from the surface of the chip, this system lets light enter the CCD at less of an angle in order to reach all the sensors more equally. Four Thirds cameras require Four Thirds lenses, and the first camera to employ the system was the Olympus E-1. Other participants include Leica Camera, Panasonic, Fuji Photo Film, Sigma Corporation and Sanyo.

Micro Four Thirds - Smaller SLR Cameras
Introduced in 2008, the Micro version relies on the LCD screen for preview rather than the common through-the-lens view in a full-size DSLR. The mirror is thus eliminated, which reduces the distance between the lens mount and the sensor and enables a slimmer profile DSLR to be built. See mirrorless camera.

Micro lenses are 6mm smaller; however, with an adapter ring, the larger Four Thirds lenses can also be used. For more information, visit www.four-thirds.org. See DSLR.