Four Thirds system

"4/3" redirects here. For 4:3 image aspect ratio, see Aspect ratio (image)#4:3 standard.

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 to cover the standard. Proponents describe it as an open standard, but companies may only use it 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 significantly 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. However, with the smaller sensor The Four Thirds System has crop factor (focal length multiplier) of about 2, and while this enables longer focal length for greater magnification, it doesn't aid the manufacture of wide angle lenses. The smaller sensor area puts it at a disadvantage against other DSLRs, especially for low light photography, and also for image quality in general. The Four Thirds system does, however, give a marked improvement over compact point and shoot digital cameras in these areas.

Sensor size and aspect ratio

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

Sizes of the sensors used in most current digital cameras relative to a standard 35mm frame.

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. Incidentally, the imaging area of a Four Thirds sensor is almost identical to that of 110 film.

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 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.

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 true DSLR in the world.^[8]

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.
• 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.
• A smaller sensor can make it easier to achieve a deeper depth-of-field with a relatively larger aperture when needed, reducing the risk of out-of-focus photos. This effect does cut both ways however, leaving the photographer somewhat less in control of DOF (see disadvantage below).

Disadvantages

• Small sensors suffer from some compromises in image quality. Smaller pixels, to match the pixel count of larger chips leads to lower dynamic range. The sensor performance of Four Thirds remains reasonably close to APS-C. However, full-frame 35mm sensors—which are nearly 4x larger—outperform Four Thirds sensors by a wide margin.^[9]
• Because of the higher crop factor, an image shot at a given relative aperture and angle of view has more depth of field on Four Thirds.^[10] 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 closing down the aperture by two stops; but it may be more difficult or impossible for a Four Thirds system to match the shallow depth of field of a 35mm full frame camera with fast lenses.
• Olympus may focus its future developments on Micro Four Thirds rather than Four Thirds.^{[citation needed]}

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.

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.

Four Thirds system cameras

The majority of Four Thirds system cameras (and Four Thirds lenses) are made by Olympus. Many Four Thirds cameras use "sensor-shift" in-body image stabilization, making the need for image stabilization technology in its lenses unnecessary. 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.^[11][12]

• 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)^[13]
• Olympus E-620 (March 2009)^[14]
• Olympus E-450 (March 2009)
• Olympus E-5 (September 2010)

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.^[15]

• 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 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.^[16][17] The Zuiko Digital lenses are well regarded for their consistently good optics.^[18] The following is a table of all current Zuiko Digital lenses:^[19]

	Wide angle	Standard	Telephoto	Super telephoto	Special-purpose
Standard	9–18 1:4–5.6	14–42 1:3.5–5.6 14–45 1:3.5–5.6 17.5–45 1:3.5–5.6 25 1:2.8 "pancake"	40–150 1:3.5–4.5 40–150 1:4–5.6	70–300 1:4–5.6 macro	35 1:3.5 macro 18-180 1:3.5-6.3 superzoom
High Grade	11–22 1:2.8–3.5	12–60 1:2.8–4 14–54 1:2.8–3.5	50–200 1:2.8–3.5		50 1:2 macro 8 1:3.5 fisheye
Super High Grade	7–14 1:4	14–35 1:2	35–100 1:2 150 1:2	90–250 1:2.8 300 1:2.8

• 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 designed 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. These are manufactured and sold by Panasonic.

An official list of available lenses can be found on Four-Thirds.org web site.^[20]

Micro Four Thirds system

Concept Micro Four Thirds camera by Olympus

Main article: Micro Four Thirds system

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.

See also

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

References

1. ^ "Kodak and Olympus join forces". DPReview.com (DPReview.com). 2001-02-13. http://www.dpreview.com/news/0102/01021301kodakolympus.asp. Retrieved 2007-11-07. 
2. ^ "Benefits". Four Thirds Consortium. http://www.four-thirds.org/en/about/benefit.html. Retrieved 2008-12-10. "Details of the Four Thirds System standard are available to camera equipment manufacturers and industry organizations on an NDA basis. Full specifications cannot be provided to individuals or other educational/research entities." 
3. ^ ^{a b} "No more compromises: The Four Thirds Standard". Olympus Europe. http://www.olympus-europa.com/consumer/dslr_7045.htm. Retrieved 2009-04-17. 
4. ^ The Four Thirds Standard. Four Thirds Consortium. 2008. http://www.four-thirds.org/en/about/standard.html. Retrieved 2009-04-17 
5. ^ Four Thirds Standard Whitepaper. Four Thirds Consortium. 2009. http://www.four-thirds.org/en/fourthirds/whitepaper.html. Retrieved 2009-10-09 
6. ^ G1 sensor vs GH1 sensor Diagram by Björn Utpott
7. ^ Knaur Interview October 01, 2002.
8. ^ Olympus E400 Digital Camera Review letsgodigital.org
9. ^ Full Frame Sensor vs Crop Sensor – Which is Right For You? Digital Photography School
10. ^ Digital SLRs and Depth of Field DOFMaster
11. ^ "DPReview E-30 conclusions page". 2009-04-09. http://dpreview.com/reviews/olympuse30/page34.asp. 
12. ^ "DPReview E-510 review". 2009-04-09. http://dpreview.com/reviews/olympuse510/. 
13. ^ Ragnarsson, Jón (2008-11-03). "Olympus E-30 officially launched". http://4-3system.com/modules/news/article.php?storyid=143. Retrieved 2008-11-03. 
14. ^ "Olympus introduces new E-620 interchangeable lens type digital SLR". 2009-02-24. http://olympus-global.com/en/news/2009a/nr090224e620e.cfm. 
15. ^ Wrotniak lens list.
16. ^ "Olympus E-System Zuiko Digital Interchangeable Lens Roadmap" (PDF). Olympus UK. Archived from the original on 2007-10-15. http://web.archive.org/web/20071015011727/http://www.olympus.co.uk/consumer/images/E-System_Lens_Roadmap.pdf. Retrieved 2007-11-29. 
17. ^ "SLRgear Olympus Lens Tests". http://www.slrgear.com/reviews/showcat.php/cat/7. 
18. ^ "Olympus Zuiko 12–60mm 1:2.8–1:4 lens review". DPReview. http://www.dpreview.com/lensreviews/olympus_12-60_2p8-4_o20/page4.asp. 
19. ^ "Olympus lens list". Asia.olympus-imaging.com. http://asia.olympus-imaging.com/products/dslr/lenses/. Retrieved 2009-08-20. 
20. ^ Four Thirds Official lens list.

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