What is Four Thirds?

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This page needs quite a lot of updating!

An inspired designed for digital and legacy-free system camera standard[edit]

"Four Thirds" is a standard set up by Olympus that was, from the start in 2003, aimed to create a manufacturer-agnostic system camera platform. Olympus actively invited manufacturer partners to join them and produce cameras and lenses conforming to Four Thirds standards. To date, Four Thirds has attracted Panasonic Lumix and its technical partner, Leica Camera, as camera partners, and Sigma Corporation as a lens manufacturing partner. Panasonic Lumix has also produced Four Thirds lenses with both its and the Leica brand. Other names that formally joined the Four Thirds consortium included Sanyo, Fujifilm, and Kodak.

Mirrorless Micro Four Thirds[edit]

Four Thirds continues today but its development has largely been eclipsed by a direct off-shoot, Micro Four Thirds, launched in 2008 and developed by Panasonic Lumix and which inherited many of the ideals and technical fundamentals of Four Thirds, with one major difference: Micro Four Thirds is mirrorless, with a new Compact System Camera (CSC) category of cameras created. By getting rid of the reflex mirror in DSLRs, including Four Thirds DSLRs, the lens mount is closer to the sensor, enabling lens and camera designs to be be even more compact. However, Micro Four Thirds employs the same Four Thirds sensor standard and much backwards compatibility with Four Thirds lenses, via adapters, is retained. Both Panasonic Lumix and Olympus now dominate the CSC market and have been joined by competing systems from Samsung, Sony, Pentax, Nikon and, lastly, Canon.

For specific details about Micro Four Thirds please visit the FTU Wiki Knowledge Base page that specifically covers this subject.

Designed for digital[edit]

The Four Thirds camera system remains the only consumer DSLR camera platform featuring interchangeable lenses that is not based on system standards from the film era. It specifies key aspects of the design of camera bodies and lenses including the lens mount, dimensions of the sensor and image circle projected by the lens.

Clarification of 'Four Thirds'[edit]

By default, Four Thirds (and Micro Four Thirds) cameras have used a frame aspect ratio of 4:3, which is loosely known as 'four thirds' format. Other popular frame aspect ratios include 3:2 (most other DSLRs and 35mm film format), square format 1:1 (some medium format cameras), and 16:9 - widescreen video/TV format. While Four Thirds cameras tend to use the 4:3 aspect ratio, this is a coincidence and 'Four Thirds' actually refers to a Videcon imaging tube size that accommodates an image circle of diameter 21.6mm, which is exactly half that of the image circle encompassing the corners of a 35mm 'full' frame (3:2 aspect ratio).

So the message is that while 4:3 aspect ratio is the normal default for Four Thirds and Micro Four Thirds cameras, the standard does not limit the manufacturer to 4:3 aspect ratio. Indeed, Panasonic has produced two cameras that have a user-selectable frame aspect ratios thanks to an over-sized Multi Aspect Ratio Four Thirds sensor.

Smaller and lighter cameras and lenses[edit]

The most often touted advantages of the Four Thirds standard are a smaller lens size and near-telecentric lenses:

Four Thirds lenses can be smaller as the diagonal of the image circle is approximately 50% of a 35mm frame. This creates a focal length crop factor of 50%; the practical upshot of which is that a lens of a given focal length has a field of view half that compared to if it was mounted on a 35mm film (or digital sensor) camera. For example, 150mm Four Thirds lens gives the view of a 300mm lens on a 35mm film camera. This has obvious benefits for sports and nature photographers. Conversely, a wide angle lens of, say, 14mm, only has the field of view of a 28mm lens fitted to a full frame camera.

The physical size and weight of a camera lens is loosely linked to its focal length and maximum (widest) aperture. In general, a Four Thirds 300mm f/2.8 lens will be roughly the same size and weight as a full frame 300mm f/2.8 lens. However, the Four Thirds lens 'sees' the same field of view as a full frame lens double its focal length. So you would need a 600mm f/2.8 full frame lens with the same viewing 'power' as a Four Thirds 300mm f/2.8. Because Micro Four Thirds cameras don't have a long 'flange/back' distance like DSLRs, or the distance between the film/sensor plane and the lens mount, Micro Four Thirds lenses can be even smaller than Four Thirds ones, especially for wide angle lenses.

Transmission brightness is not affected by the difference in image circle size, so an aperture of f/2.8, for example, on a Four Thirds lens will be exactly the same brightness as f/2.8 on any other camera platform, regardless of sensor size.

However, depth of field, the distance in front of and behind the subject that is in sharp focus, will be greater for a Four Thirds lens of equivalent field of view and aperture setting.

Telecentric lenses are those that project the light in a straight path directly towards the imager. The combination of high quality lenses and projecting an image circle bigger than the sensor allows the light that reaches it to be almost all following a direct path. This means that conformant lenses exhibit less corner shading (vignetting) than is usual.

Four Thirds and Micro Four Thirds consortium partners[edit]

Four Thirds[edit]

  • Fujifilm
  • Kodak
  • Leica Camera AG
  • Olympus
  • Panasonic Lumix
  • Sanyo
  • Sigma Corporation

Sanyo (now owned by Panasonic) was a major OEM manufacturer of digital cameras, once reportedly to be the biggest digital stills camera manufacturer, by volume, in the world. Sanyo has served as a component and OEM manufacturer for Olympus. However, no obvious practical contribution has been revealed from Fujifilm. Kodak, until 2007, was the main supplier of CCD image sensors for Four Thirds cameras. The Olympus E-400 was the last Four Thirds camera to use a Kodak CCD sensor. Even before that in 2006, Olympus launched its LiveMOS sensor brand for MOS-type sensors made by Panasonic, starting with the Olympus E-330. Panasonic also used the LiveMOS brand and more recently this brand has also been applied to sensors made by Sony. Sigma is a major independent manufacturer of system camera lenses. Although not publicly discussing the topic, Sigma is also known to be an important OEM manufacturer for several camera brands, including Olympus and probably Panasonic.

Nissin, Metz, and others are manufacturers of products, like flash guns, that are compatible with Four Thirds cameras.

Micro Four Thirds[edit]

  • Carl-Zeiss
  • Leica Camera AG
  • Olympus
  • Panasonic Lumix
  • Samyang
  • Schneider Kreuznach
  • Sigma Corporation
  • SLR Magic
  • Tamron
  • Tokina (Kenko)

Nissin, Metz, and others are manufacturers of products, like flash guns, that are compatible with Micro Four Thirds cameras.

Sony is an OEM manufacturer of imaging sensors for both Olympus and Panasonic Micro Four Thirds cameras.

The official website of Four Thirds is available here.