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Four Thirds logo

The Four Thirds system is a standard created by Olympus and Kodak for digital single-lens reflex camera (DSLR) design and development.^[1]

The system provides a standard that, with digital cameras and lenses available from multiple manufacturers, allows for the interchange of lenses and bodies from different manufacturers. U.S. Patent 6,910,814 seems^{[citation needed]} to cover the standard. This is claimed to be an open standard; it is however only accessible to companies and under a non-disclosure agreement.^[2]

Unlike older SLR systems, Four Thirds has been designed from the ground up to be entirely digital. Many lenses are extensively computerized, to the point that Olympus offers firmware updates for many of them. Lens design has been tailored to the requirements of digital sensors, most notably through telecentric designs. The size of the sensor is slightly smaller than for most DSLRs and this implies that lenses, especially telephoto lenses, can be smaller. For example, a Four Thirds lens with a 300 mm focal length would cover about the same angle of view as a 600 mm focal length lens for the 35 mm film standard, and is correspondingly more compact. That is, the Four Thirds System is said to have a crop factor (focal length multiplier) of about 2.

[edit] Sensor size and aspect ratio

Drawing showing the relative sizes of sensors used in most current digital cameras, including Four Thirds System

The name of the system stems from the size of the image sensor used in the cameras, which is commonly referred to as a 4/3" type or 4/3 type sensor. The common inch-based sizing system is derived from vacuum image-sensing video camera tubes, which are now obsolete. The imaging area of a Four Thirds sensor is equal to that of a video camera tube of 4/3" diameter. ^[3]

The usual size of the sensor is 18×13.5 mm (22.5 mm diagonal), with an imaging area of 17.3×13.0 mm (21.63 mm diagonal)^[3][4]. The sensor's area is about 30–40% smaller than the APS-C sensors used in most other DSLRs, but still around 9 times larger than the 1/2.5" sensors typically used in compact digital cameras.

The emphasis on the 4:3 image aspect ratio sets Four Thirds apart from other DSLR systems, which usually adhere to the 3:2 aspect ratio of the traditional 35 mm format. However, the standard only specifies the sensor diagonal, thus Four Thirds cameras using the standard 3:2 aspect ratio would be possible^[5]; notably newer Panasonic Micro Four Thirds models even offer shooting at multiple aspect ratios while maintaining the same image diagonal. For instance, the Panasonic GH1 uses a multi-aspect sensor which is designed to maximize use of the image circle at 4:3, 3:2, and 16:9; each ratio having a diagonal of 22.5mm.^[6]

Sensor aspect ratio has an impact on lens design. For example, many lenses designed by Olympus for the Four Thirds system contain internal rectangular baffles or permanently mounted "petal" lens hoods that optimise their operation for the 4:3 aspect ratio.^{[citation needed]}

In an interview John Knaur, a Senior Product Manager at Olympus, stated that "The FourThirds refers to both the size of the imager and the aspect ratio of the sensor".^[7] He also pointed out the similarities between 4:3 and the standard printing size of 8×10 as well as medium format 6×4.5 and 6×7 cameras, thus explaining Olympus' rationale on choosing 4:3 rather than 3:2.

[edit] Advantages, disadvantages and other considerations

An Olympus E-420, sold with a very thin "pancake" lens. The E-4XX series is advertised as the smallest DSLR in the world^[8].

[edit] Advantages

• The smaller sensor size makes possible smaller and lighter camera bodies and lenses. In particular, the Four-Thirds system allows for the development of impressive f/2.0 zoom lenses, which would be prohibitively heavy, expensive, and difficult to design for larger sensor formats.
• Telecentric optical path means that light hitting the sensor is traveling perpendicular to the sensor, resulting in brighter corners, and most importantly improved off-center resolution, particularly on wide angle lenses. This has made it easier for Four-Thirds cameras to retain high quality optics even in cheaper lenses.^{[citation needed]}
• Because the flange focal distance is significantly shorter than most mounts (such as Canon FD, Canon EF, Nikon F and Pentax K), lenses for many other SLR types, including the old Olympus OM System, can be fitted to Four Thirds cameras with simple mechanical adapter rings. (Such mechanical adapter rings typically require manual setting of focus and aperture). In many cases this produces excellent results, especially with longer focal-length lenses and lenses at smaller apertures. A series of tests by John Foster (Using OM legacy lenses on E1 body) provides a demonstration.

[edit] Disadvantages

• Small sensors suffer from some compromises in image quality. Less sensor area to collect light results in lower signal-to-noise ratio. These compromises manifest themselves as lower dynamic range, and noisier high-ISO output. The sensor performance of Four Thirds remains reasonably close to APS-C; test results show that the consumer-level E-620 is comparable to APS-C cameras at ISO 800 and below, and slightly worse at ISO 1600 and above. Full-frame 35mm sensors outperform both Four Thirds and APS-C by a wide margin.
• A telecentric optical path means more aggressive retrofocus design for wide and normal lenses, which makes wide aperture wide and normal lenses harder to design. Currently, there are only two lenses shorter than 30mm with apertures brighter than f/2: The very costly Panasonic/Leica 25mm f/1.4 and the Sigma 24mm f/1.8 Macro.
• Because of the higher crop factor, an image shot at a given relative aperture and angle of view will have more depth of field on Four Thirds. This results in less control over depth of field, compared to larger formats. For instance, a 35mm full frame dSLR can match the depth of field of a Four Thirds camera by simply closing the aperture down two stops. On the other hand, it may be more difficult or impossible for a Four Thirds system to match the depth of field of a 35mm full frame camera with fast lenses.

[edit] Differences

• Most Four Thirds cameras (notably those manufactured by Olympus) use an aspect ratio of 4:3 rather than 3:2; newer models offer cropping to 3:2, but this results in a reduced image diagonal (i.e., the effective crop factor is then 2.08). However, some Four Thirds cameras offer shooting at different aspects (including 3:2) while maintaining the same diagonal angle, for example the Panasonic Lumix DMC-GH1.

[edit] Four Thirds system companies

As of the 2006 Photo Marketing Association Annual Convention and Trade Show, the Four Thirds consortium consists the following companies:

• Fuji
• Kodak
• Leica
• Olympus
• Panasonic
• Sanyo
• Sigma

This does not imply a commitment to end user products by each company. Currently only Leica, Olympus, and Panasonic have bodies. Olympus and Leica/Panasonic make dedicated Four Thirds lenses, and Sigma makes adapted versions of their "DC" lenses for APS-C format DSLRs. Kodak once sold sensors to Olympus for use in their Four Thirds bodies, but the newer Olympus Four Thirds cameras use Panasonic sensors.

[edit] Four Thirds system cameras

The majority of Four Thirds system cameras (and Four Thirds lenses) are made by Olympus. As Olympus does not incorporate image stabilization technology into its lenses, many Four Thirds cameras utilize "sensor-shift" in-body image stabilization. All Four Thirds cameras also incorporate an automatic sensor cleaning device, in which a thin glass filter in front of the sensor vibrates at 30 kHz causing dust to fall off and adhere to a piece of sticky material below. Olympus' E-system camera bodies are noted for their inclusion of a wide range of firmware-level features and customization, good JPEG engine, and compact size. Because of the smaller format of Four Thirds, the viewfinders tend to be smaller than on comparable cameras.^[9][10]

• Olympus E-1 (November 2003)
• Olympus E-300 (December 2004)
• Olympus E-500 (September 2005)
• Olympus E-330 (January 2006)
• Panasonic Lumix DMC-L1 (February 2006)
• Leica Digilux 3 (September 2006)
• Olympus E-400 (September 2006)
• Olympus E-410 (April 2007)
• Olympus E-510 (June 2007)
• Panasonic Lumix DMC-L10 (October 2007)
• Olympus E-3 (November 2007)
• Olympus E-420 (May 2008)
• Olympus E-520 (June 2008)
• Olympus E-30 (November 2008)^[11]
• Olympus E-620 (March 2009)^[12]
• Olympus E-450 (March 2009)
• Olympus E-600 (August 2009)

[edit] Four Thirds system lenses

Four lenses for the Four Thirds system. These are three Olympus zooms (40–150 mm, 11–22 mm and 14–54 mm) and a Sigma prime (30 mm).

The Four Thirds lens mount is specified to be a bayonet type with a flange focal distance of 38.67 mm.

There are currently around three dozen lenses for the Four Thirds system standard.^[13]

• Olympus produces about 20 lenses for the Four Thirds system under Zuiko Digital brand. They are divided into three "grades" (Standard, High Grade and Super High Grade). High Grade lenses have faster maximum apertures but are significantly more expensive and larger, and the Super High Grade grade zooms have constant maximum aperture over the full zoom range; all but the Standard grade are weather-sealed. Lenses within each grade cover the range from wide-angle to super telephoto.^[14][15] The Zuiko Digital lenses are well-regarded for their consistently good optics.^[16] The following is a table of all current Zuiko Digital lenses:^[17]

 14–45 1:3.5–5.6 17.5–45 1:3.5–5.6 25 1:2.8 "pancake" 

• Olympus also makes 1.4× and 2× teleconverters and an electronically-coupled extension tube.
• Sigma has adapted 13 lenses for the Four Thirds system, ranging from 10 to 800 mm, including several for which no equivalent exists: the fast primes (30 mm f/1.4 and 50 mm f/1.4) and extreme telephoto (300–800 mm f/5.6).
• Leica has made four lenses for the Four Thirds system: fast and slow normal zooms and a 14–150 mm super-zoom, all with Panasonic's image stabilization system, and an unstabilized f/1.4 25 mm prime.

An official list of available lenses can be found on Four-Thirds.org web site.^[18]

[edit] Micro Four Thirds system

Concept Micro Four Thirds camera by Olympus

In August 2008, Olympus and Panasonic introduced a new format: Micro Four Thirds.

The new system uses the same sensor, but removes the mirror box from the camera design. A live view preview is shown on either the camera's main LCD or via an electronic viewfinder, as in digital compact cameras. Autofocus is accomplished via a contrast-detect process using the main imager, again similar to digital compact cameras. The goal of the new system is to allow for even smaller cameras, competing directly with higher-end point-and-shoot compact digital cameras and lower-end DSLRs. The smaller flange focal distance allows for more compact normal and wideangle lenses.

Four Thirds lenses can be used on Micro Four Thirds bodies with an adapter.

[edit] See also

• Lenses for SLR and DSLR cameras
• Lens mount
• List of lens mounts
• Micro Four Thirds system

[edit] References

[edit] External links

• Official Four Thirds System site
• Four Thirds US patent 6,910,814; PDF version (1.7 MiB)
• Andrzej Wrotniak's pages about the Four Thirds System – includes a complete lens list
• Spanish site about the Four Thirds System
• Four Thirds User – independent site and user-community dedicated to the Four Thirds system, including Micro Four Thirds

v • d • e Four Thirds System lenses timeline

Wide-angle Standard Telephoto Super Telephoto 4.5 7 8 9 10 11 12 14 17.5 18 20 22 24 25 30 35 40 42 45 50 54 55 60 70 90 100 105 125 135 150 180 200 250 300 400 500 800 2003 Olympus Zuiko Digital 14-54mm F2.8-3.5 Olympus Zuiko Digital 50mm F2.0 Macro Olympus Zuiko Digital 50-200mm F2.8-3.5 2004 Olympus Zuiko Digital 11-22mm F2.8-3.5 Olympus Zuiko Digital 14-45mm F3.5-5.6 Sigma 18-50mm F3.5-5.6 DC Sigma 18-125mm F3.5-5.6 DC Olympus Zuiko Digital 40-150mm F3.5-4.5 Sigma 55-200mm F4-5.6 DC Olympus Zuiko Digital ED 150mm F2.0 Olympus Zuiko Digital ED300mm F2.8 2005 Olympus Zuiko Digital ED 7-14mm F4.0 Olympus Zuiko Digital 17.5-45mm F3.5-5.6 Olympus Zuiko Digital 35mm F3.5 Macro Olympus Zuiko Digital ED 35-100mm F2.0 Olympus Zuiko Digital ED 90-250mm F2.8 2006 Olympus Zuiko Digital 8mm F3.5 Olympus Zuiko Digital ED 14-42mm F3.5-5.6 Leica D Vario-Elmarit 14-50mm F2.8-3.5 ASPH Sigma 18-50mm F2.8 EX DC Olympus Zuiko Digital ED 18-180mm F3.5-6.3 Sigma 24mm F1.8 EX DG Sigma 30mm F1.4 EX DC HSM Olympus Zuiko Digital ED 40-150mm F4.0-5.6 Sigma 50-500mm F4-6.3 EX DG HSM Sigma 105mm F2.8 EX DG Macro Sigma 150mm F2.8 EX DG APO Macro HSM 2007 Olympus Zuiko Digital ED 12-60mm F2.8-4.0 SWD Leica D Vario-Elmar 14-50mm F3.8-5.6 ASPH Leica D Summilux 25mm F1.4 ASPH Olympus Zuiko Digital ED 70-300mm F4.0-5.6 Sigma 135-400mm F4.5-5.6 DG APO Sigma 300-800mm F5.6 EX DG HSM APO 2008 Olympus Zuiko Digital ED 9-18mm F4.0-5.6 Sigma 10-20mm F4.0-5.6 EX DC HSM Olympus Zuiko Digital ED 14-35mm F2.0 SWD Olympus Zuiko Digital 14-54mm F2.8-3.5 II Leica D Vario-Elmar 14-150mm F3.5-5.6 ASPH Olympus Zuiko Digital 25mm F2.8 Sigma 50mm F1.4 EX DG HSM Olympus Zuiko Digital ED 50-200mm F2.8-3.5 SWD 2009 Sigma 70-200mm F2.8 EX DG Macro II HSM 20?? Sigma 4.5mm F2.8 EX DC HSM Sigma 10mm F2.8 EX DC HSM Sigma 50-150mm f2.8 II APO EX DC HSM Green background indicates lenses with image stabilization. Red background indicates unconfirmed lenses (rumors, please edit).