- Four Thirds System
The Four Thirds System is a standard created by Olympus and
Kodak fordigital single-lens reflex camera (DSLR) design and development.cite news | first= | last= | coauthors= | title=Kodak and Olympus join forces | date=2001-02-13 | publisher=DPReview.com | url =http://www.dpreview.com/news/0102/01021301kodakolympus.asp | work =DPReview.com | pages = | accessdate = 2007-11-07 | language = ] (Four Thirds is a registered trademark of Olympus Optical Co., Ltd.)The system provides a standard that, with
digital camera s and lenses available from multiple manufacturers, allows for the interchange of lenses and bodies from differentmanufacturer s. US patent|6910814 seems to cover the standard. Four Thirds is not anopen standard , however, as it does not meet the "allowing anyone to use" criterion commonly accepted as the definition of an open standard.Fact|2007-07-28|date=July 2007Unlike older SLR systems, Four Thirds has been designed from the ground up to be entirely digital. 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 (see drawing below) 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 acrop factor (focal length multiplier) of about 2.Sensor size and aspect ratio
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-sensingvideo camera tube s, 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 18×13.5 mm (22.5 mm diagonal), with an imaging area of 17.3×13.0 mm (21.6 mm diagonal). cite web|url=http://www.olympus-europa.com/consumer/dslr_7045.htm |title=No more compromises: The Four Thirds Standard |accessdate=2007-11-09 |work=Olympus Europe ] Its area is 30–40% less than the
APS-C sensors used in most other DSLRs, but around 9 times larger than the 1/2.5" sensors typically used incompact digital camera s (seeimage sensor format ).The Four Thirds system uses a 4:3 image aspect ratio, in common with compact digital cameras. 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 for the sensor proportions is that it has historically been the standard for
television and became a dominant aspect ratio for computer monitors, as found in theVGA ,SVGA ,XGA ,SXGA+ ,UXGA andQXGA 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 optimise 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". [http://web.archive.org/web/20021205033057/http://www.a-digital-eye.com/Olympus43Q&A.html Knaur] Interview October 01, 2002.] He goes on to state the similarity between 4:3 and the standard printing size of 8×10, as well as medium format 6×4.5 and 6×7 cameras.
Mechanical considerations
The Four Thirds
lens mount is specified to be a bayonet type with aflange focal distance of 38.67 mm.Advantages, disadvantages and other factors
Advantages
* 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 series bodies, in the kit lenses sold with the E-4x0 and E-5x0 bodies, and in longer telephoto lenses.
* 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 can be fitted to Four Thirds cameras with simple mechanical adapter rings. (Such mechanical adapter rings typically require manual setting of focus and aperture). Lenses made for the Olympus OM System can also be used, in some cases with excellent results. However, in general, longer focal length and "normal" aperture lenses (as opposed to "fast", extra-large aperture lenses) seem to produce the best results. A series of tests by John Foster ( [http://www.biofos.com/cornucop/omz_e1.html Using OM legacy lenses on E1 body] ) provides a demonstration.
* Although in no way related to the Four Thirds standard in itself, there is the current advantage that all Four Thirds cameras have the Olympus
Supersonic Wave Filter (SSWF) dust reduction system, generally regarded to be the bestdust reduction system available Fact|date=September 2008.Disadvantages
* Smaller sensors are generally more prone to noise. Noise typically becomes more pronounced at high ISO exposures, meaning that picture quality may suffer in low light situations where the ISO has to be increased above 400. [cite web| date =February, 2008| title =Olympus E-3 Review, February 2008, Simon Joinson| publisher =Digital Photography Review|url=http://www.dpreview.com/reviews/olympuse3/|accessdate =2008-02-22]
* A telecentric optical path means more aggressive retrofocus design for wide lenses, which makes them bigger, and makes wide apertures harder to achieve.
Other factors
The following two factors can be considered to be advantages under certain circumstances and disadvantages under other circumstances.
* The smaller sensor means that the
depth of field is greater than for cameras with a larger sensor. See for a discussion of this aspect. Compared to a 35mm or full frame camera the depth of field is approximately twice as great. Compared to most other DSLR cameras that use APS-C size sensors the depth of field for a Four Thirds camera is approximately 25% greater.:Whether this greater depth of field is an advantage or disadvantage depends on the desired effect. For taking portraits or other pictures where the subject is to be isolated from the background (by blurring the background) it is a disadvantage. For landscape, telephoto and macro photography, and most point-and-shoot photography, it is an advantage.
:Note that for a camera with a larger sensor it is possible to increase the depth of field by reducing lens aperture, although this will require a longer shutter time and/or an increased ISO setting, which may be problematic for certain situations. The reverse consideration is not applicable: a Four Thirds System camera cannot decrease its minimum DOF to match a larger sensor camera.
* The aspect ratio of pictures taken with a Four Thirds camera is 4:3, while all other DSLR cameras and full frame 35mm film cameras take pictures with an aspect ratio of 3:2. Nearly all compact digital cameras take pictures with a 4:3 aspect ratio.
: For traditional print and frame sizes that have an aspect ratio of 3:2 (6×4", 9×6", 12×8") this is a disadvantage for Four Thirds cameras as 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.
: Some other traditional print sizes (5×7", 8×10", 11×14") 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 or have large matting to meet these sizes. The same applies for pictures to be used on standard PC screens and non-HDTV television screens.
Four Thirds system companies
As of the
2006 Photo Marketing Association Annual Convention and Trade Show , the Four Thirds consortium consists the following companies (inalphabet ical order):* Fuji
* Kodak
* Leica
* Olympus
* Panasonic
*Sanyo
* SigmaThis should not be interpreted as a commitment to end user products by each company. Up to now, only Leica, Olympus and Panasonic have bodies, and Leica, Olympus and Sigma have lenses in the market. Kodak, for example, has sensors to sell to body makers.
Four Thirds System cameras
*
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)Four Thirds System lenses
There are currently around three dozen lenses for the Four Thirds System standard. [http://www.wrotniak.net/photo/oly-e/lenses.html Wrotniak] lens list.]
* Olympus is producing about 20 lenses for the Four Thirds System under
Zuiko Digital brand. Focal lengths range from 7 to 300 mm (14–600 mm in35 mm equivalent focal length ), and include macros. cite web|url=http://www.olympus.co.uk/consumer/images/E-System_Lens_Roadmap.pdf |title=Olympus E-System Zuiko Digital Interchangeable Lens Roadmap |accessdate=2007-11-29 |publisher=Olympus UK ]
* Sigma has adapted 12 lenses for the Four Thirds System, ranging from 10 to 800 mm.
* 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|link=yes 25 mm prime.
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