The Four Thirds System is a standard created by Olympus and Eastman Kodak for digital single-lens reflex camera (DSLR) and mirrorless camera design and development.[1]
The system provides a standard that, with digital cameras and lenses available from multiple manufacturers, allows for the interchange of lenses and bodies from different manufacturers. U.S. Patent 6,910,814 seems to cover the standard. Proponents describe it as an open standard, but companies may only use it under a non-disclosure agreement
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