A standard for digital single lens reflex (SLR) 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. For more information, visit www.four-thirds.org. See DSLR.