The Micro Four Thirds sensor

By m43lab.com·June 20, 2026·8 min read

Micro Four Thirds (M43) uses a sensor that measures 17.3 × 13 mm, giving it a 2× crop factor relative to 35mm full frame. It was co-developed by Panasonic and Olympus and introduced in 2008 as the basis for a shared, open lens mount standard. Every M43 body from any manufacturer, including Panasonic, OM System, and Blackmagic, accepts every M43 lens.

Sensor dimensions and crop factor

The crop factor describes how many times smaller the sensor diagonal is compared to 35mm full frame (43.3mm diagonal). M43 has a 21.6mm diagonal, giving a crop factor of exactly 2×. This affects two things in practice: the field of view a given focal length produces, and the depth of field at a given aperture.

A 25mm lens on M43 gives the same field of view as a 50mm lens on full frame. An f/1.2 aperture on M43 produces the same depth of field as approximately f/2.4 on full frame. These are not disadvantages. They are trade-offs that make telephoto reach easier and depth of field more manageable for certain subjects.

How it compares to other sensors

The diagram below shows each sensor format drawn to relative scale, nested so you can see the real size differences at a glance. Micro Four Thirds is highlighted. Hover or tap any format to see its dimensions and crop factor.

Sensors are drawn to relative scale from published dimensions. Micro Four Thirds measures 17.3 × 13 mm (225 mm²); full frame is roughly 3.8× the area. Crop factor is relative to 35mm full frame.

What the sensor size affects

Light gathering and noise

A larger sensor collects more total light at any given f-stop, which helps with noise at high ISO. Full frame has roughly 3.8× the sensor area of M43. In practice this means M43 sensors are typically 1.5 to 2 stops behind full frame at high ISO, though this gap has narrowed substantially with modern sensor designs. The Panasonic G9 II and OM System OM-1 II both perform competitively at ISO 3200 and above.

Depth of field

M43's 2× crop factor means that to match the depth of field of a full-frame lens at a given aperture, you divide by 2. A 45mm f/1.2 on M43 gives the same field of view and similar depth of field to a 90mm f/2.4 on full frame. This makes M43 lenses with wide apertures genuinely useful for subject separation, and makes deep focus easier to achieve without stopping down.

Lens size and system weight

The smaller image circle required by M43 allows lenses to be physically smaller and lighter. This is one of the main reasons the system exists. A weather-sealed fast prime on M43 weighs roughly half what the equivalent full-frame lens would weigh. For travel, wildlife at distance, and any situation where carrying a large kit is impractical, the weight saving is real and significant.

Telephoto reach

The 2× crop factor multiplies the effective focal length of every lens. A 300mm lens on M43 frames like a 600mm lens on full frame. Combined with the availability of relatively affordable telephoto lenses, this makes M43 an unusually effective system for birds, wildlife, and sports at a fraction of the cost and weight of full-frame telephoto setups.

The open standard

Micro Four Thirds is an open standard, meaning any manufacturer can make bodies and lenses that are fully compatible with each other. This is defined in the formal MFT standard agreement signed by Panasonic and Olympus (now OM Digital Solutions) in 2008. Third-party brands including Sigma, Viltrox, and TTArtisan make lenses that work natively on all M43 bodies without adapters.

The mount has a 44mm diameter and a 19.25mm flange distance. The short flange distance makes it straightforward to adapt lenses from virtually any other system, including full frame, APS-C, and cinema mounts, using passive adapters.

Current sensor technology in M43

The OM System OM-1 and OM-1 Mark II use a stacked BSI sensor with phase detection autofocus across the full sensor area. Stacking moves the support circuitry behind the photodiode layer, which increases readout speed and reduces rolling shutter on video and fast-moving subjects. The OM-1 II also introduced a quad-Bayer arrangement (two million physical pixels, each split into four) that enables multi-shot modes capable of producing 50MP images through pixel-shift.

The Panasonic G9 II uses a standard Live MOS sensor with phase detection AF, not a stacked design. It still achieves strong readout performance for its class, but the architecture differs from the OM System flagship approach.

Micro Four Thirds sensor generations

Micro Four Thirds resolution has climbed in clear steps since the format launched in 2008, moving from 12 megapixels to 16, then 20, and most recently 25 megapixels. The physical sensor size has never changed: every generation keeps the 17.3 × 13 mm imaging area and the 2× crop factor. What changed across generations was pixel count, readout speed, autofocus, and stabilisation support. The summary below is drawn from the documented sensor history in the Wikipedia Micro Four Thirds article.

The 12 megapixel era (2008 to 2012)

The first Micro Four Thirds sensor debuted in the Panasonic G1 in September 2008 at 12 megapixels. This generation powered the early Panasonic G, GF, and GH bodies and the first wave of Olympus PEN cameras. A multi-aspect variant in the Panasonic GH1 used a slightly larger sensor so the diagonal stayed constant when switching between 4:3, 3:2, and 16:9 aspect ratios.

The 16 megapixel era (2010 to 2015)

Sixteen megapixel sensors arrived in 2010 and became the workhorse resolution for the format through several revisions. A Sony-sourced 16 megapixel sensor used in the Olympus E-M5 marked a clear jump in image quality, and the fourth-generation 16 megapixel chip in the Olympus E-M1 introduced on-sensor phase-detection autofocus to the system for the first time.

The 20 megapixel era (2015 onward)

Twenty megapixels became the standard in 2015 with the Panasonic GX8 and spread across both Panasonic and Olympus flagships. In 2022 the OM System OM-1 introduced a back-side illuminated (BSI) stacked 20 megapixel sensor with quad-pixel phase detection, the most significant architectural change in the format since phase-detect AF.

The 25 megapixel era (2022 onward)

The current top resolution arrived with the Panasonic GH6 in 2022, followed by the Panasonic G9 II in 2023, which became the first Panasonic Micro Four Thirds body with phase-detection autofocus. This is the highest native resolution shipped in a standard Micro Four Thirds sensor to date.

Generations at a glance

The following table lists the main sensor generations in chronological order, with representative cameras and the headline technology each introduced.

Years and resolutions above reflect the documented generations in the source article. Pixel counts are the effective, marketed resolution; the multi-aspect and quad-pixel sensors use a higher physical pixel count than the marketed figure.

How M43 compares to other systems