In general, lens exchangeable digital SLR cameras use currently existing lenses designed for 35mm film SLR cameras, and as a result require large image sensors such as a CCD, in sizes similar to those of 35mm or APS films. With large sized image sensors in 35mm or APS size, however, the difference in optical properties such as insufficient luminosity around the perimeter of the imaging sensor becomes troublesome even though light beams with high entry angles are sufficient for film, the elimination of color bleeding (especially noticeable with wide angle lenses) is necessary through the use of high resolution lenses to satisfy the micro-meter sized pitch of image sensors, which all adds up to the optical design of a large lens.

We fine tuned the balance of image quality, size, and system expandability and finalized on the best combination being a 4/3 size imaging sensor.
By using lenses designed exclusively for the 4/3 size digital system, we achieved unprecedented high image quality and mobility.