View source for Micro Four Thirds

[[File:Micro.Four.Thirds.Logo.png|upright=.7|thumb|right|Official Micro Four Thirds logo]]
The '''Micro Four Thirds''' system (abbreviated variously as M43, M4/3, μ4/3 or MFT) is a standard introduced in 2008, for the design and development of mirrorless interchangeable lens digital cameras and lenses. The system was jointly developed by [[Olympus]] and [[Panasonic]], but the Micro Four Thirds alliance has since grown to include over 40 companies.

The name 'Micro Four Thirds' differentiates it from its predecessor, the [[camerapedia:Four Thirds system|Four Thirds system]] — the Micro Four Thirds system employs a [[mirrorless]] design, as opposed to the more traditional single-lens reflex (SLR) format of Four Thirds. This design allows M43 cameras and lenses to be more compact than the DSLR Four Thirds designs.

[[File:Olympus (9506191565).jpg|upright=1.4|thumb|right|Olympus E-M5 with three lenses]]
While Micro Four Thirds is an open standard, the partner companies control access to the design specifications for creating supported equipment as well as the use of the Micro Four Thirds trademarks and logos.

== History ==
The Micro Four Thirds (M43) standard was announced by [[Olympus]] and [[Panasonic]] on August 5, 2008.<ref name="M43_announcement_DPR">{{cite web |last1=Butler |first1=Richard |title=Olympus / Panasonic announce Micro Four Thirds |url=http://www.dpreview.com/articles/4821964954/microfourthirds |website=[[w:Digital Photography Review|DPReview]] |access-date=2021-09-16 |archive-url=https://web.archive.org/web/20140817224642/http://www.dpreview.com/articles/4821964954/microfourthirds |archive-date=2014-08-17 |date=August 5, 2008 |url-status=live}}</ref>

The first M43 camera was the stills-only, DSLR-styled [[Panasonic Lumix DMC-G1]], introduced on September 8, 2008.<ref name="G1_announcement_DPR">{{cite web |title=Exclusive: Panasonic Lumix G1 previewed |url=https://www.dpreview.com/articles/2644209767/panasonic-dmc-g1 |website=[[w:Digital Photography Review|DPReview]] |access-date=2021-09-16 |archive-url=https://web.archive.org/web/20140805120708/http://www.dpreview.com/articles/2644209767/panasonic-dmc-g1 |archive-date=2014-08-05 |date=September 12, 2008 |url-status=live}}</ref> This was followed five months later by the hybrid [[Panasonic Lumix DMC-GH1]] which added the ability to capture 1080/24p or 720/60p video in a similar DSLR-style body.<ref name="GH1_PR">{{cite web |title=The CREATIVE HD HYBRID from the LUMIX G Micro System The DMC-GH1 – With D-SLR Photo Quality and Full-HD Movies |url=http://panasonic.net/avc/lumix/popup/pressrelease/gh1.html |website=[[Panasonic|Panasonic Global]] |archive-url=https://web.archive.org/web/20110928225434/http://panasonic.net/avc/lumix/popup/pressrelease/gh1.html#1 |archive-date=2011-09-28 |date=March 3, 2009 |url-status=dead}}</ref>

Olympus's first M43 offering, the [[Olympus PEN E-P1]] was introduced a few months after the GH-1, in June of 2009. The E-P1 offered a different styling take which eliminated the viewfinder in favor of a more [[w:Rangefinder camera|rangefinder-esque]] design, somewhat similar to the overall ergonomics offered by the company's existing compact camera line.<ref name="E-P1_PR">{{cite web |title=Introduction of OLYMPUS PEN E-P1 Micro Four Thirds interchangeable lens system camera |url=http://www.olympus-global.com/en/news/2009a/nr090616ep1e.html |website=[[Olympus|Olympus Global]] |access-date=2021-09-27 |archive-url=https://web.archive.org/web/20110925025711/http://www.olympus-global.com/en/news/2009a/nr090616ep1e.html |archive-date=2011-09-25 |date=June 16, 2009 |url-status=live}}</ref>

{{As of|2021}}, the M43 consortium includes over 40 companies.<ref>{{cite web |title=Supporting Companies/Contact |url=https://www.four-thirds.org/en/contact/ |website=Micro Four Thirds (official website) |access-date=2021-09-16 |archive-url=https://web.archive.org/web/20210812145957/https://www.four-thirds.org/en/contact/ |archive-date=2021-08-12}}</ref>

== Design specification ==
[[File:Flange Focal Length (2 types camera).PNG|upright=.75|thumb|Flange Focal Length (DSLR vs mirrorless)]]
M43 shares the same sensor size as Four Thirds. But the mirrorless design eliminates the mirror box and optical viewfinder allowing a shorter [[w:flange focal distance|flange focal distance]], which is the distance from the lens mount and the sensor (see image at right) — the M43 flange focal distance is 20mm, compared to Four Thirds' 40mm. The M43 bayonet lens mount also has a throat size which is 6mm smaller in diameter than that of Four Thirds. Both of these design choices allow for more compact bodies and lenses. The third major change is that the M43 lens mount spec has eleven electrical contacts, two more than the earlier system. Adapters are available to mount Four Thirds lenses on M43 cameras with full electronic control, including autofocus.<ref name="M43_Benefits">{{cite web |title=Micro Four Thirds: Benefits of Micro Four Thirds |url=http://www.four-thirds.org/en/microft/index.html |website=Four-Thirds Consortium |archive-url=https://web.archive.org/web/20111020153903/http://www.four-thirds.org/en/microft/index.html |archive-date=2011-10-20 |url-status=dead}}</ref>

One major tenet of the Four Thirds design philosophy that carries over to M43 is that lenses should be as close to [[w:Telecentric lens|telecentric]] as feasible. That is, the light from the lens should reach the sensor at as close to a right angle as possible. This concept of enhancing the linearity of light hitting the sensor minimizes ghosting, flaring, vignetting, chromatic aberration and/or loss of sharpness that can sometimes be caused by light encountering the sensor photocell at an acute angle.<ref name=43_Benefits>{{cite web |title=Four Thirds: Benefits of Four Thirds |url=http://www.four-thirds.org/en/fourthirds/index.html |publisher=Four Thirds Alliance (official website) |archive-url=https://web.archive.org/web/20120104135146/http://www.four-thirds.org/en/fourthirds/index.html |archive-date=2012-01-04 |url-status=dead}}</ref> While Four Thirds and M43 lenses are not technically telecentric, this philosophy ensures that they are closer to the ideal than are lenses developed for most other systems, although some more recent mirrorless systems from Canon and Nikon appear to adopt this goal as well.<ref>{{cite web |last1=Wong |first1=Robin |title=Telecentric Lens Design - Did Canon RF and Nikon Z Adopt Similar Approach as Micro Four Thirds? |url=https://robinwong.blogspot.com/2019/08/telecentric-lens-design-did-canon-rf.html |archive-url=https://web.archive.org/web/20200618130636/https://robinwong.blogspot.com/2019/08/telecentric-lens-design-did-canon-rf.html |archive-date=2020-06-18 |date=August  19, 2019 |url-status=dead}}</ref>

The elimination of the mirror box means that the image is composed based on a representation created by the image sensor itself, either on an LCD display or an electronic viewfinder (EVF). This means that the image you see is exactly the image you capture. This Live View photography style also allows seamless switching between capturing images and video.<ref name="MicroFourThirds_Standard">{{cite web |title=Micro Four Thirds: Standard |url=http://www.four-thirds.org/en/microft/whitepaper.html |website=Four Thirds Alliance (official website) |archive-url=https://web.archive.org/web/20120104150207/http://www.four-thirds.org/en/microft/whitepaper.html |archive-date=2012-01-04 |url-status=dead}}</ref>

== Image sensor ==
The name 'Four Thirds' is derived from the fact that the size of the [[w:image sensor|image sensor]] is categorized as {{fraction|4|3}} inch.<ref name="FT_Sensor">{{cite web |title=Four Thirds System |url=http://www.four-thirds.org/en/about.html |website=Four-Thirds.org |publisher=[[Olympus]] |archive-url=http://web.archive.org/web/20030805204513/http://www.four-thirds.org/en/about.html |archive-date=2003-08-05 |url-status=dead}}</ref><ref name="FT_slideshow">{{cite web |title=Four Thirds System |url=http://www.four-thirds.org/en/pdf/FourThirdsSystem.pdf |website=Four-Thirds.org |publisher=[[Olympus]] |archive-url=http://web.archive.org/web/20040719055454/http://www.four-thirds.org/en/pdf/FourThirdsSystem.pdf |archive-date=2007-07-09 |format=PDF |url-status=dead}}</ref> The {{glossary link|glossary=Glossary of photographic terms|aspect ratio}} of the sensor, meaning the ratio of the width of the sensor to its height, is 4:3. This differentiates the specification from other digital systems including so-called "[[w:full frame|full frame]]" and [[w:APS-C|APS-C]] sized sensors from brands such as [[w:Nikon|Nikon]], [[w:Canon EOS|Canon]], [[w:Sony α|Sony]], [[w:Fujifilm X series|Fujifilm]] or [[w:Pentax|Pentax]]) as well as from [[w:135 film|35mm film]], all of which produce an image with an aspect ratio of 3:2 which was inherited from analog TV standards.

The actual size of the Four Thirds sensor — as defined in the Four Thirds system white paper — is 18mm × 13.5mm, with an imaging area of 17.3×13 mm. This gives the image a diagonal length of 21.6 mm; the smallest of the common APS-C sensors used has a diagonal of 24.88 mm with dimensions of 20.7×13.8 mm.
[[Image:SensorSizes.svg|thumb|upright=.75|left|Sizes of the sensors used in most current digital cameras relative to a standard 35mm frame]]
The diagonal length of the 4/3rds sensor is roughly half that of a 35mm film negative.

=== Equivalence  ===
The ratio of the image size, combined with the smaller sensor means that cameras with a Four Thirds sensor have a 'crop factor' of exactly 2x — that is to say, a 50mm lens for a 35mm film or a so-called "full frame" digital camera adapted to use on a M43 body gives the equivalent field of view to a 100mm lens on a "full frame" camera. The term "crop factor" is somewhat misleading as the sensor does not crop the image at all — it simply utilises a smaller section of the lens. In essence only the portion of light entering the lens that actually hits the sensor is altered, meaning the field of view is smaller, and thereby effectively doubling the focal length of the lens.

This "crop factor" ''does'' affect the apparent [[w:depth of field|depth of field]] of the captured image: with the magnification of 2, the DOF is effectively doubled. This perceived effect is due to the FOV "crop"; the same depth of field is present, but you are viewing it at twice the magnification.

It is important to note that neither the light gathering ability of the lens, nor any of its traits are ''actually'' altered: a 50mm {{f/}}2 lens on a M43 camera has the same f-stop and depth of field as a similar on a 35mm camera, but the 4/3rds sensor records only the portion of the image (i.e. the field of view) that would be captured by a 100mm lens on the larger sensor. As a general rule of thumb the depth of field of a lens is halved as its focal length is doubled (if the aperture remains constant). The end result is therefore that a M43 camera has twice the depth of field as a 35mm camera with a lens covering the same field of view.

Returning to the above example, a 50mm {{f/}}2 "full frame" lens used on a M43 body is effectively equal to a  camera with a 100mm lens set at f/4.

As a further example of the above, let us compare cameras using M43, APS-C and "full frame" sensors in a given situation with the goal of producing an image with a similar [[w:Angle of view|angle of view]], [[w:Depth of field|depth of field]], [[w:Diffraction-limited system|diffraction limitation]] and [[w:Motion blur|motion blur]] from the same vantage point:
{| class="wikitable zebra"
![[w:Image sensor format|Image sensor format]]
!Focal length
!F-number at<br />same depth of field
!ISO speed at<br />same exposure time
!Shutter speed for<br />same motion blur
|-
| style="text-align:center" | '''[[Micro Four Thirds|M43]]''' || style="text-align:center" | '''50&nbsp;mm''' ||style="text-align:center" | '''2.0''' || style="text-align:center" | '''200'''|| style="text-align:center" | '''1/200 sec.'''
|-
| style="text-align:center" | [[w:APS-C|APS-C]] || style="text-align:center" | 66&nbsp;mm || style="text-align:center" | 2.8 || style="text-align:center" | 360|| style="text-align:center" | 1/200 sec.
|-
| style="text-align:center" | [[w:Full-frame digital SLR|Full frame]] || style="text-align:center" | 100&nbsp;mm|| style="text-align:center" | 4.0 || style="text-align:center" | 800|| style="text-align:center" | 1/200 sec.
|}

Using the same shutter speed, all three systems above would have the same exposure, the same depth of field, and the same field of view. The smaller sensor size of the M43 allows a lower ISO to be used at the same shutter speed; the doubling of the depth of field allows a two-stop advantage in sensitivity for the same end result.

This allows a photographer to either use a lens at a lower F-stop (for faster shutter speeds) or shoot at a lower ISO (for lower noise in the final image) than would be possible in 35mm or APS-C format. This field of view/depth of field effect was a primary consideration in the design of the Four-Thirds system.<ref name="43_Benefits" />

=== Live MOS sensor ===
Live MOS is a brand name for Four Thirds {{glossary link|glossary=Glossary of photographic terms|image sensor}}s. This technology debuted in 2006 with the [[camerapedia:Four Thirds|Four Thirds]] [[w:Olympus E-330|Olympus E-330]], [[w:Panasonic Lumix DMC-L1|Panasonic Lumix DMC-L1]] and [[w:Leica Digilux 3|Leica Digilux 3]].<ref name="DPR_E-330-review">{{cite web |last1=Askey |first1=Phil |title=Olympus E-330 EVOLT Review |url=https://www.dpreview.com/reviews/olympuse330/ |website=Digital Photography Review |access-date=2021-10-13 |archive-url=https://web.archive.org/web/20060319061004/http://www.dpreview.com/reviews/olympuse330/ |archive-date=2006-03-19 |date=March 18, 2006 |url-status=live}}</ref> As the name implies it offers a {{glossary link|glossary=Glossary of photographic terms|live view}} using a [[w:Metal Oxide Semiconductor|Metal Oxide Semiconductor (MOS)]] sensor. Specifically, the Live MOS sensor is a type of [[w:NMOS logic|NMOS]] device.

Olympus claimed the new sensor could achieve similar image quality to {{glossary link|glossary=Glossary of photographic terms|CCD}}-based sensors while also providing the energy-saving attributes of a {{glossary link|glossary=Glossary of photographic terms|CMOS}} device.<ref name="DPR_E-330-review" /> In order to combat the disadvantage of CMOS devices when it comes to image {{glossary link|glossary=Glossary of photographic terms|noise}}, the Live MOS chip integrates noise-reduction technology.

== Lenses ==
{{Main|Micro Four Thirds lenses}}
The principles outlined above in the design of the Four Thirds sensor also carry over into the lens designs for the system: with a crop (or magnification) factor of two, a telephoto lens for the M43 system with the same field of view that of a lens designed for 35mm can be half the size.

For example, a 150mm lens fitted to a M43 body produces the same field of view (and therefore effectively the same magnification) as a 300mm lens on a 35mm film (or "full frame" digital) camera. Not only does this mean M43 lenses can be significantly smaller than their "full frame" counterparts, it also means it is much easier and cheaper to produce lenses with good focal length to f-stop ratios.

Most M43 lenses are also nearly [[w:Telecentric lens|telecentric]], meaning that no matter what angle the light enters the lens, the glass within the lens is designed to ensure the beams of light hit the sensor straight on. This design requirement is due to the nature of digital sensors: they are highly sensitive to the angle at which light hits them, with highly angled photons not being picked up by the sensor at all.

The diameter of the M43 lens mount is just under twice the diagonal of the imaging sensor, which also allows for improvements in lens design: with the lens focusing the image down to just over half the area of the mount throat before it hits the sensor, this allows the lenses to be brighter without sacrificing the size or weight advantages gained by the smaller sensor.

== Camera bodies ==
{{Main|Micro Four Thirds cameras}}
{{As of|2021}}, nearly seventy cameras models have been produced for the system. The two main Micro Four Thirds partners, Olympus and Panasonic, have created the bulk of these. The rest were produced by the likes of Kodak, JVC, Black Magic, DJI, Z Cam and Yi.

== External Links ==
* [https://www.four-thirds.org/en/microft/ Micro Four Thirds] pages.
* [https://www.mu-43.com/ Mu-43] - The most active forum for Micro Four Thirds users.
* [https://www.youtube.com/watch?v=m072i-jDSg4&t=1s The TRUTH about the MICRO FOUR THIRDS System (M4/3 vs Full Frame)] - This video from Gerald Undone has a good explanation for the derivation of the Four Thirds name. It also generally does a good job discussing the strengths and weaknesses of M43 relative to other systems. Note, though, that his discussion of [[depth of field]] and [[bokeh]] is flawed.

== Sources ==
{{reflist}}

[[Category:Micro Four Thirds]]