The is a standard released by Olympus Imaging Corporation and Panasonic in 2008, for the design and development of mirrorless interchangeable lens digital cameras, camcorders and lenses. Camera bodies are available from Blackmagic, DJI, JVC, Kodak, Olympus, OM System, Panasonic, Sharp, Logitech Mevo and Xiaomi. MFT lenses are produced by Cosina Voigtländer, Kowa, Kodak, Mitakon, Olympus, Panasonic, Samyang, Sharp, Sigma, SLR Magic, Tamron, Tokina, TTArtisan, Veydra, Xiaomi, Laowa, Yongnuo, Zonlai, Lensbaby, Venus Optics and 7artisans amongst others.

The specifications of the MFT system inherit the original sensor format of the Four Thirds system, designed for DSLRs. However, unlike Four Thirds, the MFT system design specification does not require lens telecentricity, a parameter which accommodated for the inaccurate sensitivity to off-angle light due to the geometry of the photodetectors of contemporary image sensors. Later improvements in manufacturing capabilities enabled the production of sensors with a lower stack height, improving sensitivity to off-angle light, eliminating the necessity of telecentricity and decreasing the distance from the image sensor at which a lens's rear element could be positioned without compromising light detection. Such a lens, however, would eliminate the room necessary to accommodate the mirror box of the single-lens reflex camera design, and would be incompatible with SLR Four Thirds bodies.

Micro Four Thirds reduced the specified flange focal distance from 38.67mm to 19.25mm. This reduction facilitates smaller body and lens designs, and enables the use of adapters to fit almost any lens ever made for a camera with a flange distance larger than 19.25mm to a MFT camera body. Still-camera lenses produced by Canon, Leica, Minolta, Nikon, Pentax and Zeiss have all been successfully adapted for MFT use, as well as lenses produced for cinema, e.g., PL mount or C mount.

Comparison with other systems

For comparison of the original Four Thirds with competing DSLR system see Four Thirds system#Advantages, disadvantages and other considerations

Compared to inexpensive digital compact cameras and many bridge cameras, MFT cameras have better, larger sensors, and interchangeable lenses. There are many lenses available. On top of this, a large number of other lenses (even from the analogue film era) can be fitted using an adapter. Different lenses yield greater creative possibilities. However, Micro Four Thirds cameras also tend to be slightly larger, heavier and more expensive than compact cameras.

Compared to most digital SLRs, the Micro Four Thirds system (body and lenses) is smaller and lighter. However, their sensors are smaller than full-frame or even APS-C systems. The small lenses do not allow the noise depth-of-field tradeoffs of larger lenses in other systems. Many, but not all Micro Four Thirds cameras use an electronic viewfinder (EVF). Resolutions and refresh speeds on these EVF displays were originally compared negatively to optical viewfinders, but today's EVF systems are faster, brighter and much higher resolution than the original displays. Original Micro Four Thirds cameras used a contrast-detection autofocus system, slower than the phase-detect autofocus that is standard on DSLRs. To this day, most Micro Four Thirds cameras continue to use a contrast-based focusing system. Although some current models, such as the Olympus OM-D E-M1 Mark II, feature a hybrid phase-detect/contrast detect system, Panasonic Lumix cameras continued to use a contrast-based system called DFD (Depth from Defocus) until the release of the G9 II in 2023. Both systems today provide focusing speeds to rival or even surpass many current DSLRs.

Sensor size and aspect ratio

The image sensor of Four Thirds and MFT measures 18 mm × 13.5 mm (22.5 mm diagonal), with an imaging area of 17.3 mm × 13.0 mm (21.63 mm diagonal), comparable to the frame size of 110 film. Its area, ca. 220 mm2, is approximately 30% less than the APS-C sensors used in other manufacturers' DSLRs; it is around 9 times larger than the 1/2.3" sensors typically used in compact digital cameras.

The Four Thirds system uses a 4:3 image aspect ratio, like compact digital cameras. In comparison, DSLRs usually adhere to the 3:2 aspect ratio of the traditional 35 mm format. Thus, "Four Thirds" refers to both the size and the aspect ratio of the sensor. However, the chip diagonal is shorter than 4/3 of an inch; the 4/3 inch designation for this size of sensor dates back to the 1950s and vidicon tubes, when the external diameter of the camera tube was measured, not the active area.

The MFT design standard also specifies multiple aspect ratios: 4:3, 3:2, 16:9 (the native HD video format specification), and 1:1 (a square format). With the exception of a few MFT cameras, most MFT cameras record in a native 4:3 format image aspect ratio, and through cropping of the 4:3 image, can record in 16:9, 3:2 and 1:1 formats.

+Micro Four Thirds sensor generations Sensor Specifications ISO Dynamic range Camera models PDAF IBIS Features Released 12 Mpx Gen 1 13 Mpx, 4000x3000 effective 100-3200 8EV (-5.0/+3.0) Panasonic G1, G2, G10, GF1, GF2; Olympus E-P1, E-P2, E-P3, E-PL1, E-PL2, E-PL3, E-PM1 No Olympus only SSWF September 2008 (Panasonic G1) 12 Mpx Gen 2 "multi-aspect" 14 Mpx, 4000x3000 effective 100-3200 7.8EV (-4.8/+3.0) Panasonic GH1 No No SSWF, multi-aspect March 2009 16 Mpx Gen 1 "multi-aspect" 18.3 Mpx, 4608x3456 effective 160-12800 11.3EV Panasonic GH2, G5, G6 No No SSWF, multi-aspect (GH2 only) September 2010 (Panasonic GH2) 16 Mpx Gen 2 "Sony" 17 Mpx, 4608x3456 effective 200-12800 12.3EV Olympus E-M5, E-P5, E-PL5, E-PM2; Panasonic GH3 No Olympus only SSWF February 2011 (Olympus E-M5) 16 Mpx Gen 3 16.6 Mpx, 4592x3448 effective 160-12800 10.5EV Panasonic GX1, GF6, G3 No No SSWF May 2011 (Panasonic G3) 12 Mpx Gen 3 13 Mpx, 4000x3000 effective 160-6400 10.1EV Panasonic GF3, GF5 No No SSWF June 2011 (Panasonic GF3) 16 Mpx Gen 4 17 Mpx, 4608x3456 effective 200-25600 12.7EV Panasonic GH4, G7, G80, GX7; Olympus E-M1, E-M5II, E-M10, E-M10II, E-M10III EM1 only Yes (except GH4 and G7) SSWF, No AA filter (G80) March 2013 (Olympus PEN E-PL5) 20 Mpx Gen 5 22 Mpx, 5184x3888 effective 200-25600 12.5EV Panasonic G9, G90, GX8 Olympus E-M1 II, E-M1 III, E-M5 III, PEN-F, OM-System OM-5 Olympus EM1, EM5 and OM-5 Only Yes SSWF July 2015 (Panasonic GX8) 25 Mpx Gen 6 25 Mpx (Rev.2) Gen 6 27 Mpx, 5776x4336 effective 100-25600 13EV Panasonic GH6 Panasonic G9 II (Rev.2) G9 II Only Yes SSWF February 2022 (Panasonic GH6) September 2023 (Panasonic G9 II) 20 Mpx "BSI" Gen 6 23 Mpx, 5184x3888 effective 200-25600 12.5EV OM-System OM-1 Yes Yes SSWF March 2022

Lens mount

The MFT system design specifies a bayonet type lens mount with a flange focal distance of 19.25 mm. By avoiding internal mirrors, the MFT standard allows a much thinner camera body.

Viewfinding Viewing is achieved on all models by live view on electronic displays with LCD screens. In addition, some models feature a built-in electronic viewfinder (EVF), while others may offer optional detachable electronic viewfinders. An independent optical viewfinder typically matched to a particular non-zoom prime lens is also an option.

Backward compatibility The throat diameter is about 38 mm, 6 mm less than that of the Four Thirds system. Electrically, MFT uses an 11-contact connector between lens and camera, adding to the nine contacts in the Four Thirds system design specification. Olympus claims full backward compatibility for many of its existing Four Thirds lenses on MFT bodies, using a purpose built adapter with both mechanical and electrical interfaces..

Adapters to other lens mounts The shallow but wide MFT lens mount also allows the use of existing lenses including Leica M, Leica R, and Olympus OM system lenses, via Panasonic and Olympus adapters. Aftermarket adapters include Leica Screw Mount, Contax G, C mount, Arri PL mount, Praktica, Canon, Nikon, and Pentax, amongst others. In fact, almost any still camera, movie or video camera interchangeable lens that has a flange focal distance greater than or marginally less than 20 mm can often be used on MFT bodies via an adapter. While MFT cameras can use many of these "legacy" lenses only with manual focus and manual aperture control mode, hundreds of lenses are available, even those designed for cameras no longer in production.

While lens manufacturers seldom publish lens mount specifications, the MFT mount has been reverse-engineered by enthusiasts, with CAD files available.

Autofocus design Until 2013, MFT cameras exclusively used contrast-detection autofocus (CDAF), a common autofocus system for mirrorless compact or "point-and-shoot". By comparison, DSLRs use phase-detection autofocus (PDAF). The use of separate PDAF sensors has 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 Four Thirds lenses focus on Micro Four Thirds proficiently when an electrically compatible adapter is used on the Micro Four Thirds cameras, and they focus on Micro Four Thirds cameras much quicker than earlier generation Four Thirds lenses can.

Some MFT cameras, beginning with the Olympus OM-D E-M1 in 2013, incorporate phase-detection hardware on the sensor. Besides offering faster autofocus speed, these camera bodies perform better with legacy lenses (e.g. focus performance of the 150mm f/2 and 300mm f/2.8 lenses are as quick and accurate as a native Four Thirds body). The Panasonic G9 II is the first micro four thirds camera from Panasonic which has phase detect autofocus.

Flange focal distance and crop factor The much shorter flange focal distance enabled by the removal of the mirror allows normal and wide angle lenses to be significantly smaller because they do not have to use strongly retrofocal designs.

The Four Thirds sensor format used in MFT cameras is equivalent to a 2.0 crop factor when compared to a 35 mm film (full frame) camera. This means that the field of view of an MFT lens is the same as a full frame lens with twice the focal length. For example, a 50 mm lens on a MFT body would have a field of view equivalent to a 100 mm lens on a full frame camera. For this reason, MFT lenses can be smaller and lighter because to achieve the equivalent 35 mm film camera field of view, the MFT focal length is much shorter. See the table of lenses below to understand the differences better. For comparison, typical DSLR sensors, such as Canon's APS-C sensors, have a crop factor of 1.6.

Equivalents