Micro Four Thirds System - Autofocus Design

Autofocus Design

The MFT system design specifies the use of contrast-detection autofocus (CDAF) which is a common autofocus system for compact or "point-and-shoot". By comparison, virtually all DSLRs use a different autofocus system known as phase-detection autofocus (PDAF). The use of separate PDAF sensors has long been favored in DSLR systems because of mirror box and pentaprism design, along with better performance for fast-moving subjects.

The (non-Micro) Four Thirds system design standard specifies a 40 mm flange focal length distance, which allowed for using a single lens reflex design, with mirror box and pentaprism. Four Thirds DSLR cameras designed by Olympus and Panasonic initially used exclusively PDAF focusing systems. Olympus then introduced the first live view DSLR camera, which incorporated both traditional DSLR phase focus and also optional contrast detection focus. As a result, newer Four Thirds system lenses were designed both for PDAF and contrast focus. Several of the latter Four Thirds lenses focus on Micro Four Thirds proficiently when an electrically compatible adapter is used on the Olympus and the later Panasonic Micro Four Thirds cameras, and they focus on Micro Four Thirds cameras much quicker than earlier generation Four Thirds lenses can.

At the announcement of the MFT system design standard it was suggested that the powerful focusing motors required for contrast-detection autofocus by compact cameras and MFT may not operate properly on at least some of the existing Four Thirds lenses designed for phase-detection autofocus.

Many PDAF Four Thirds system lenses, when using adapters with proper electrical connections on Micro Four Thirds cameras, do focus much more slowly than "native" designed MFT lenses. Some Four Thirds bodies do not focus as quickly as others, or as accurately as does contrast focus. This is a downside of phase focus, which can shift focus to the front or behind the calculated focus position for each lens. Micro Four Thirds will also focus Four Thirds lenses faster than a Four Thirds camera focuses using the Four Thirds "Live View" focus. Most Four Thirds lenses still work on Micro Four Thirds, and the relative speed will depend on the camera model and the lenses used. Overall, native Micro Four Thirds lenses focus much faster than the majority of Four Thirds lenses.

An advantage to the newly introduced MFT system designed cameras is the already-existing family of very high quality, large aperture, automatic exposure, autofocusing, and sometimes even optical image stabilized Four Thirds lenses made by Olympus, Panasonic and Leica.

The latest range of Olympus Pen cameras (the E-P3, the light E-PL3 and the new mini version) are claimed to be the fastest focusing removable lens cameras, including those which use phase technology (DSLR cameras). Comparative tests and the basis for all the speed improvements and whether the technology can track like a phase focus designed for sport applications are not yet known.