What is the Four Thirds System?

The Demise of The Four Thirds System

The 4/3 camera system was introduced by Olympus in 2003 as the ideal digital format. Since Olympus had no legacy Autofocus lenses, they were free to design a brand new system from the ground up, when they entered the DSLR market. The E1 was announced in June 2003

Olympus decided on a slightly smaller sensor format than the other camera makers were using. This smaller format promised smaller and lighter camera bodies and lenses. This system would have strong appeal for wildlife and telephoto shooters, since their lenses would be easier to carry, and probably cheaper too.

But 4/3 struggled in the DSLR marketplace, never really achieving as much as a 10% market share. And almost exactly three years ago Olympus (along with Panasonic) produced another new system, Micro 4/3, based on the same sensor format but having an entirely different lens mount.

One year ago, Olympus introduced their 4/3 flagship upgrade... the Olympus E5. At the same time they discontinued all their other 4/3 DSLRs, telling us that their goal was to "create one beautiful system" that would be based on their newer M4/3 lens mount. They also stopped developing 4/3 lenses, and Sigma, one of their 4/3 partners, discontinued ten of their fourteen 4/3 lenses.

The only problem with this concept of "one beautiful system" was that there is no real lens compatibility between the two systems. Only a small handful of 4/3 lenses could auto focus on a M4/3 body, assuming that you purchased a very expensive adapter. And no M4/3 lens could be used on a 4/3 camera. These were clearly two very different systems.

To make matters worse, there are no weather sealed M4/3 cameras or lenses. So if you need that feature, then you must either buy a three year old Olympus E3 (or the brand new $1700 E5), or just buy some other brand. And this isn't the only problem Olympus has.

    Olympus now has no entry level 4/3 camera. Olympus seems to have no 4/3 marketing plan Olympus has completely stopped developing 4/3 lenses Olympus 4/3 now has virtually no third party support Olympus' 4/3 partners seem to have vanished Olympus 4/3 is almost impossible to find in retail stores Olympus is putting all their effort into M4/3

Obviously, the 4/3 system is in the process of being abandoned, just like Olympus abandoned the OM system around a decade earlier.

M4/3 certainly is a good idea, that has huge appeal to photographers using any brand gear, since it can mount virtually any lens with one of the dozens of adapters available. But there is no compelling reason for any 4/3 user to think that M4/3 is an "upgrade" or even a continuation of 4/3.

4/3 essentially is a dead system now, which means that no new users will enter the fold. This doesn't mean that existing 4/3 cameras and lenses won't work, or won't produce excellent results. It just means we won't see very much new technology in these cameras, since there may be no new versions produced.

Olympus has hinted that they might eventually upgrade the E5, or even produce an upgrade for the E30. But unless they use a newer sensor, then we are frozen in time with a 2008 sensor that keeps getting tweaked, while the competition keeps forging ahead with newer and better sensors.

Every system has pluses and minuses.

I use Olympus 4/3 because I like the lenses, the deep feature set, and their outstanding jpegs. And at the time I first got into the system, it was a "very good value for the money."

The incredibly good, but very expensive, Olympus E5 But others prefer Olympus 4/3 because of the weather sealing on their top model and all HG and SHG lenses, or features like IBIS, pixel mapping, dustbuster, digital leveler, and AF micro adjust, even in some of their lower priced cameras.

It is just a real shame, and a disappointment that there will probably be no more affordable 4/3 cameras. And even the flagship E5 is on borrowed time, until M4/3 can assume the task.

Olympus has essentially created a flagship without a fleet.

The Four Thirds Specification defines the standard diagonal length of the 4/3-type image sensor, suitable image circle of lens and an interface between lens and body. This will make it possible to secure compatibility among camera bodies and lenses regardless of manufacturer or model.

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

"Four Thirds System. Different from older SLR and DSLR systems, Four Thirds was designed from the base up to be totally digital. Many of the lenses have been significantly computerized, to a point that companies are providing firmware updates for a large number of them. Lens designs have been adapted to digital sensor requirements, most particularly through telecentric designing. The sensor size is somewhat less than a majority of DSLR cameras which implies that lenses, more than ever a telephoto lens, can be made quite a lot smaller. As an example, a Four Thirds System lens featuring a a focal length of 300mm could cover virtually the same viewing angle as a 600mm focal length lens as a 35 mm film lens, and is equally more compact. The Four Thirds System has a focal length multiplier (crop facto) of around 2. Updated Review May 15, 2011"

Sensor size and aspect ratio

Drawing showing the relative sizes of sensors used in most current digital cameras, relative to a 35mm film frame. The name of the system comes from the size type of the image sensor used in the cameras. The image sensor 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.

The size of the sensor is 18ื13.5 mm (22.5 mm diagonal), with an imaging area of 17.3ื13.0 mm (21.63 mm diagonal). Its area is 30–40% less than the nearly APS-C sensors used in most other DSLRs, but around 9 times larger than the 1/2.5" sensors typically used in Digital Camera Review by Gene Wrights (see image sensor format).

The Four Thirds system uses a 4:3 image aspect ratio, in common with Digital Camera Review by Gene Wrights. This differs from other DSLRs which usually adhere to the 3:2 aspect ratio of the traditional 35 mm format. The Four Thirds standard specifies the aspect ratio in addition to the size of the imaging circle. Claim 1 of US patent 6,910,814 (mentioned earlier) is specific: "…said camera body having an image pickup device having an imaging range with an aspect ratio of 4:3 on an imaging surface within the image circle…"

A major reason to choose 4:3 sensor proportions was similarity to the aspect ratio on standard definition television. Computer monitors also commonly use a 4:3 aspect ratio, as found in the VGA, SVGA, XGA, SXGA+, UXGA and QXGA standards.

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 optimize their operation for the 4:3 aspect ratio.

John Knaur, a Senior Product Manager at Olympus, states that "The FourThirds refers to both the size of the imager and the aspect ratio of the sensor". He goes on to state the similarity between 4:3 and the standard printing size of 8ื10, as well as medium format 6ื4.5 and 6ื7 cameras.

Advantages, disadvantages and other factors


  • The smaller sensor size makes possible smaller and lighter camera bodies and lenses. In particular, the potential exists for very fast lenses and very high quality lenses at lower costs. Currently this is evident to some extent in the Olympus E-4x0 and E-620 bodies, in the kit lenses sold with the E-4x0 and E-5x0 bodies, and in longer telephoto lenses.
  • Greater depth of field at any given aperture and focal length due to the smaller format. This is an advantage in many applications (macro photography in particular), but a disadvantage in others (portraiture) where a shallow depth of field is desired.
  • 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 competing 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.


  • Smaller sensors collect less light in total than larger ones, and As a result have a weaker signal-to-noise ratio. Images made with a Four Thirds sensor will show more noise at the same sensitivity than those made with larger formats, although the noise performance of Four Thirds is only slightly worse than APS-C.
  • A telecentric optical path means more aggressive retro focus design for wide and normal lenses, which makes them bigger, and makes wide apertures harder to achieve.

Other factors

  • Since the practical lens aperture for a given angle of view is smaller, the minimal depth of field will be larger, providing less subject isolation.
  • The aspect ratio of pictures taken with a Four Thirds camera is 4:3, while all other DSLR cameras and full frame 35 mm film cameras take pictures with an aspect ratio of 3:2. Nearly all Digital Camera Review by Gene Wrights take pictures with a 4:3 aspect ratio.

    For traditional print and frame sizes that have an aspect ratio of 3:2 (e.g., 6ื4"), photographs will have to be cropped or printed with borders to fit these sizes. The same applies if the picture is to be used for a wide-screen application.

    Other traditional print sizes (5ื7", 8ื10", 11ื14") are closer to a 4:3 aspect ratio than they are the 3:2 aspect ratio, meaning the photographer does not need to crop as much as would a user of a 3:2 format. The same applies for pictures to be used on standard PC screens and non-HDTV television screens.

  • Four Thirds system companies

    As of the 2008 Photo Marketing Association Annual Convention and Trade Show, the Four Thirds consortium consists the following companies (in alphabetical order):

    This should not be interpreted as a commitment to end user products by each company. Up to now, only Leica, Olympus, and Panasonic have bodies. Olympus, Leica/Panasonic, and Sigma make dedicated Four Thirds lenses (the Sigma lenses are adaptations of their "DC" lenses for APS-C format DSLRs). Kodak, for example, once sold sensors to Olympus for use in their Four Thirds bodies; 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. 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. Anecdotal reports and reviews report that this system is quite effective; few users report any issues with sensor contamination.

    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. 

    • Olympus E-1 (November 2003) - Discontinued
    • Olympus E-300 (December 2004) - Discontinued
    • Olympus E-500 (September 2005) - Discontinued
    • Olympus E-330 (January 2006) - Discontinued
    • Panasonic Lumix DMC-L1 (February 2006) - Discontinued
    • Leica Digilux 3 (September 14, 2006) - Discontinued
    Four 4/3 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).

    Four Thirds system lenses

    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.

    Brand Designation FL[mm] MaxAp MinAp MFD[m] EC El/Gr A/S Wgt[g] DืL[mm] Filter Year Street
    Olympus ZD Fisheye 8 3.5 22 .135 Y 10/6 0/1 455 79ื78 - 2006 $670
    Sigma EX DG Macro 24 1.8 22 .18 ? 10/9 2/? 520 84ื88 77 2006 $340
    Leica D Summilux 25 1.4 16 .38 ? 10/9 1/4 525 78ื75 62 2007 $800
    Olympus ZD 25 2.8 22 .20 Y 5/4 1/0 95 64ื24 43 2008 $250
    Sigma EX DC HSM 30 1.4 16 .4 - 7/7 1/2 410 78ื64 62 2006 $400
    Olympus ZD Macro 35 3.5 22 .15 Y 6/6 0/0 165 71ื53 52 2005 $200
    Olympus ZD Macro 50 2.0 22 .24 Y 11/10 0/1 300 71ื62 52 2003 $425
    Sigma EX DG HSM 50 1.4                    
    Sigma EX DG Macro 105 2.8 22 .31 Y 11/10 0/0 470 55ื103 58 2006 $400
    Olympus ZD ED 150 2.0 22 1.4 Y 11/9 1/1 1610 100ื150 82 2004 $2200
    Sigma EX DG HSM APO Macro 150 2.8 22 .38 Y 16/12 0/2 920 80ื142 72 2006 $600
    Olympus ZD ED 300 2.8 22 2.0 Y 13/11 0/3 3290 129ื281 112 2004 $5700
    Brand Designation FL[mm] MaxAp MinAp MFD[m] EC El/Gr A/S Wgt[g] DืL[mm] Filter Year Price
    Olympus ZD 7-14 4.0 22 .25 Y 18/12 2/3 780 87ื120 - 2005 $1520
    Olympus ZD ED 9-18 4.0-5.6 22 .25 Y 13/9 2/1 280 80ื73 72 2008 $540
    Sigma EX DC HSM 10-20 4.0-5.6 22 .24 ? 14/10 3/3 495 84ื86 77 2008 $500
    Olympus ZD 11-22 2.8-3.5 22 .28 Y 12/10 2/0 485 75ื93 72 2004 $675
    Olympus ZD ED SWD 12-60 2.8-4.0 22 .25 Y 14/10 3/4 575 80ื99 72 2007 $900
    Olympus ZD ED SWD 14-35 2.0 22 .35 Y 18/17 2/3 915 86ื123 77 2008 $2300
    Olympus ZD ED 14-42 3.5-5.6 22 .25 * 10/8 2/1 190 66ื61 58 2006 $250
    Olympus ZD 14-45 3.5-5.6 22 .38 M 12/10 2/1 285 71ื87 58 2004 ($200)
    Leica D Vario-Elmar 14-50 3.8-5.6 22 .29 Y 15/11 2/2 434 75ื93 67 2007 (K)
    Leica D Vario-Elmarit 14-50 2.8-3.5 22 .29 Y 16/12 2/0 490 78ื103 72 2006 $900
    Olympus ZD 14-54 2.8-3.5 22 .22 Y 15/11 3/0 435 74ื88 67 2003 ($430)
    Olympus ZD II 14-54 2.8-3.5 22 .22 Y 15/11 3/0 435 74ื88 67 2008 $670
    Leica D Vario-Elmar 14-150 3.5-5.6 22 .50 ? 15/11 4/1 520 79ื90 72 2008 $1100
    Olympus ZD 17.5-45 3.5-5.6 22 .28 Y 7/7 2/0 210 71ื70 52 2005 (K)
    Sigma DC 18-125 3.5-5.6 22 .5 Y 15/14 2/1 385 70ื78 62 2004 $280
    Olympus ZD 18-180 3.5-6.3 22 .45 M 15/13 2/2 440 85ื78 62 2006 $400
    Olympus ZD ED 35-100 2.0 22 1.4 Y 21/18 0/5 1650 97ื214 77 2005 $2200
    Olympus ZD 40-150 3.5-4.5 22 1.5 Y 13/10 0/0 425 77ื107 58 2004 ($230)
    Olympus ZD ED 40-150 4.0-5.6 22 0.9 * 12/9 0/1 220 66ื72 58 2006 $280
    Olympus ZD 50-200 2.8-3.5 22 1.2 Y 16/15 0/3 920 87ื157 67 2003 ($830)
    Olympus ZD ED SWD 50-200 2.8-3.5 22 1.2 Y 16/15 0/3 995 87ื157 67 2008 $1200
    Sigma EX DG HSM APO 50-500 4.0-6.3 22 1.0-3.0 Y 20/16 ?/4 1830 95ื224 86 2006 $1000
    Sigma Apo II EX DG Macro HSM 70-200 2.8 22 1.0 ? 18/15 0/5 1385 87ื190 77 2009 ?
    Olympus ZD ED 70-300 4.0-5.6 22 1.2 M 14/10 0/3 615 80ื127 58 2007 $400
    Olympus ZD ED 90-250 2.8 22 2.5 Y 17/12 0/3 3270 124ื276 105 2005 $5500
    Sigma DG APO 135-400 4.5-5.6 32 2.0-2.2 ? 13/11 1/3 1280 84ื189 77 2007 ($590)
    Sigma EX DG HSM APO 300-800 5.6 32 6.0 ? 18/16 0/2 5915 157ื549 [7] 2007 $8000
    Brand Designation FL[mm] MaxAp MinAp MFD[m] EC El/Gr A/S Wgt[g] DืL[mm] Filter Year Price


    In case some of the acronyms I'm using in table headers are not quite clear:

    • FL is the actual focal length in millimeters. The EFL (35-mm film equivalent) is twice this value.
    • MaxAp stands for the maximum lens aperture (smallest F-number); MinAp — for the minimum aperture.
    • When two numbers are shown with a hyphen, the first one refers to the zoom at the widest setting, and the second — at the longest one.
    • MFD is the minimum focus distance in meters.
    • EC shows the compatibility with the EC-14 teleconverter (see below): Y (yes, including autofocus), M (manual focus only), - (none). This is based mostly on Olympus data, with an asterisk denoting a positive based on users' feedback. (In such cases, AF may actually be working, if not up to Olympus specs, speed- and accuracy-wise.)
    • El/Gr stands for the number of elements and element groups in the lens design.
    • A/S shows the number of elements with aspherical surfaces and using special (low or extra low) dispersion glass. Both kinds are usually a sign of quality (especially for wide-angle lenses), and may raise the cost considerably.
    • Wgt is the weight, as per manufacturer's published specs.
    • DืL are lens dimensions (diameter and length), rounded to the nearest millimeter.
    • Filter specifies the front filter thread (mm).
    • Year refers to when the lens became (or is expected to become) available on the market.
    • Price — as quoted by a selected merchant (usually B&H) at the time I last checked. Prices, obviously, vary with time and between merchants, so consider this column only as a rough guide.

    For lenses no longer in production prices are shown in parentheses, like ($200), these are the latest I have seen while the lens was still current. (K) instead of the price means that the lens is (or was) available only in a kit with a camera body.

    Olympus is producing about 20 lenses for the Four Thirds system under Zuiko Digital brand. These are divided into three "grades" (Standard, Pro, Top Pro). The higher grade lenses have faster maximum apertures but are significantly more expensive and larger, and the Top Pro 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 entire range from ultra-wide-angle to super-telephoto. The Zuiko Digital lenses are well-regarded by reviewers for their consistently good optics. The following is a table of all current Zuiko Digital lenses:

      Wideangle Standard Telephoto Supertelephoto Special-purpose
    Standard 9–18 1:4–5.6 14–42 1:3.5–5.6

    25 1:2.8 "pancake"

    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

    Pro 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

    Top Pro 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 1.4ื and 2ื teleconverters and an electronically-coupled extension tube. Sigma has adapted 12 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 (50–500 mm f/4–6.3). 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

    Micro Four Thirds system

    Concept Micro Four Thirds camera by OlympusIn 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 Digital Cameras and lower-end DSLRs. The smaller flange focal distance allows for more compact normal and wide-angle lenses.

    Four Thirds lenses can be used on Micro Four Thirds bodies with an adapter. Many do not support contrast-detect autofocus and must be manually focused.

    Micro Four Thirds SystemMicro Four Thirds system cameras

    As of August 2009, only Olympus and Panasonic have a commitment to the Micro Four Thirds system.

    The first Micro Four Thirds system camera was Panasonic Lumix DMC-G1, which was commenced in Japan in October 2008. In April 2009, Panasonic Lumix DMC-GH1 with HD video recording added to it.

    The first Olympus model, Olympus PEN E-P1 was shipped in July 2009.

    Micro Four Thirds lenses

    As of March 2010, there are ten Micro Four Thirds lenses:

    Standard zooms

    Superzooms Telephoto zooms Wideangle zooms Primes Macro lenses


    Of the six Panasonic lenses, the 7–14 mm and the 20 mm are not image stabilized. Neither of the Olympus lenses are image stabilized. Of particular interest is the 7–14 wide-angle lens – the reduced flange-focal distance of Micro Four Thirds enables such extreme wideangle lenses to be made significantly smaller and cheaper than for a traditional DSLR, because the retrofocus optical schemes can be avoided or made less extreme.

    Further, both Panasonic and Olympus manufacture an adapter to enable use of any Four Thirds lenses on Micro Four Thirds cameras. While many Four Thirds lenses accept firmware updates to enable contrast autofocusing, many others are manual-focus-only. A variety of companies manufacture adapters to use lenses from nearly any legacy lens mount[6] (such lenses, of course, support no automatic

    Four Thirds and Micro Four Thirds Lens Adapters
    Four Thirds and Micro Four Thirds Lens AdaptersHave an old lens you want to mount on your new Four Thirds System Camera? Now you can adapt Leica, Olympus, Nikon, Panasonic, Voigtlander and Four Thirds Lenses to Micro Four Thirds Cameras and Four Thirds Cameras Updated Review May 15, 2011

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