Micro Four Thirds

Micro Four Thirds, abbreviated M43 or MFT, is an open camera and lens standard introduced in 2008 by Olympus and Panasonic. The standard defines the physical lens mount dimensions, the flange focal distance (the distance from the mount face to the sensor), and the maximum image circle size. Any lens and body conforming to the M43 standard are mechanically and electronically compatible, regardless of manufacturer. The founding manufacturers opened the specification to other companies, resulting in a wide ecosystem of compatible products.

The M43 sensor measures 17.3mm x 13mm, with a diagonal of approximately 21.6mm compared to the 43.3mm diagonal of a 35mm full-frame sensor. This produces the 2x crop factor. The smaller sensor enables a smaller mount inner diameter (44mm) and a shorter flange distance (19.25mm) compared to full-frame mirrorless systems, which allows M43 camera bodies and lenses to be physically smaller and lighter than equivalent full-frame hardware.

The name derives from the Four Thirds DSLR system developed by Olympus and Kodak in 2002, which used the same sensor size but with a longer 38.67mm flange distance to accommodate a mirror box. Removing the mirror box for mirrorless design allowed the flange distance to be reduced significantly, hence Micro Four Thirds. Four Thirds DSLR lenses can be used on M43 bodies with a passive adapter, though autofocus performance with adapted Four Thirds lenses varies.

As of 2025, the primary M43 camera manufacturers are OM System (which acquired the imaging division of Olympus in 2021), Panasonic, and Blackmagic Design. Sigma, Voigtlander, Laowa, 7Artisans, TTArtisan, Viltrox, and others produce M43 mount lenses. The M43 native lens catalog covers focal lengths from 4mm fisheye to 400mm telephoto, with prime and zoom options across all common categories from multiple manufacturers.