Four Thirds System
The Four Thirds system is a digital camera standard that is currently being used by Olympus (the developer of the standard), Sigma, Leica, and Panasonic. Kodak, while developing sensors for the standard and participating in its development, does not produce cameras or lenses which support the Four Thirds system. This standard is an outgrowth of Olympus researchers' investigations into the unique aspects of the interrelationship between lenses and digital photography and consideration of the optical compromises on which existing DSLR designs were predicated.
Prior to the Four Thirds standard, digital SLR configurations were based heavily on that of their film counterparts, with little or no optimization for the issues associated with digital photography. Since digital cameras revolve around imaging sensors in the same way that film cameras depend on their film, sensor size in this format was chosen to strike a balance between image quality (which prefers a larger sensor) and portability. Concerning size, the image sensor plays a larger role than many realize, since it not only determines the size of the camera body- it affects the size of the lens, as well. Choosing a smaller format results in higher noise levels, but it also allows development of portable long zooms such as Olympus’ Zuiko Digital 70-300mm F/4.0 standard grade lens which, when converted to 35mm equivalent, has a focal range of 140-600mm in a package that is a little over a pound and only 5 inches long. The Four Thirds system design standard has also resulted in the reduction of vignetting (the brightness gradient noticeable in some images) and crosstalk (incoming light hitting adjacent sensors).
At the present time, Panasonic, Olympus, and Leica offer Four Thirds cameras, while both Sigma and Olympus offer a number of lenses for the system. Additionally, adapters are available to allow the use of legacy lenses with Four Thirds cameras. While the standard has not attracted wider corporate interest yet, the Micro Four Thirds format, if successful, may change the playing field by allowing the use of interchangeable lenses on compact cameras, blurring the line between DSLR and point-and-shoot designs and opening a new market for lens manufacturers.