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The Four Thirds System is a standard created by Olympus and Kodak for digital single-lens reflex camera (DSLR) design and development.[1] (Four Thirds is a registered trademark of Olympus Optical Co., Ltd.)
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. 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. 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 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, 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 18×13.5 mm (22.5 mm diagonal), with an imaging area of 17.3×13.0 mm (21.6 mm diagonal).[3] 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 in compact digital cameras (see image 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 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 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".[4] 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.
[edit] Mechanical considerations
The Four Thirds lens mount is specified to be a bayonet type with a flange focal distance of 38.67 mm.
[edit] Advantages, disadvantages and other factors
[edit] 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 (Using OM legacy lenses on E1 body) provides a demonstration.
[edit] 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.[5] Independent of noise reduction algorithms, the noise performance of a Four-Thirds sensor is generally regarded to be around half a stop worse than an APS-C sensor.
- A telecentric optical path means more aggressive retrofocus design for wide and normal lenses, which makes them bigger, and makes wide apertures harder to achieve.
[edit] 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 depth of field: DOF vs. format size 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.
[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 (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, and Leica, Olympus and Sigma have lenses in the market. Kodak, for example, once sold sensors to Olympus for use in their Four-Thirds bodies; the newer Olympus Four-Thirds cameras use Panasonic sensors.
[edit] Four Thirds System cameras
[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).
There are currently around three dozen lenses for the Four Thirds System standard.[7]
- 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 25 mm prime.
An official list of available lenses can be found on Four-Thirds.org web site.[10]
[edit] Micro Four Thirds System
In August 2008, Olympus and Panasonic introduced a new lens format: Micro Four Thirds
It is the first system targeted at the compact digital market, attempting to bring DSLR image quality and the flexibility of an interchangeable lens system to a wider market.
The new system uses the same sensor, but removes the mirror from the camera design. 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.
[edit] References
- ^ "Kodak and Olympus join forces", DPReview.com, DPReview.com (2001-02-13). Retrieved on 7 November 2007.
- ^ Quoted from the footnote of the page http://www.four-thirds.org/en/about/benefit.html (retrieved on 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."
- ^ "No more compromises: The Four Thirds Standard". Olympus Europe. Retrieved on 2007-11-09.
- ^ Knaur Interview October 01, 2002.
- ^ "Olympus E-3 Review, February 2008, Simon Joinson". Digital Photography Review (February, 2008). Retrieved on 2008-02-22.
- ^ Ragnarsson, Jón (2008-11-03). "Olympus E-30 offically launched". Retrieved on 2008-11-03.
- ^ Wrotniak lens list.
- ^ "Olympus E-System Zuiko Digital Interchangeable Lens Roadmap". Olympus UK. Retrieved on 2007-11-29.
- ^ "SLRgear Olympus Lens Tests".
- ^ Four Thirds Official lens list.
[edit] See also
[edit] External links
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