Four Thirds System

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Four Thirds logo
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] (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. Four Thirds is not an open standard, however, as it does not meet the "allowing anyone to use" criterion commonly accepted as the definition of an open standard.[citation needed]

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. In common terms the Four Thirds System is said to have a focal length magnification factor of exactly 2. Although use of this terminology is debatable because the Four Thirds System is not based upon 35 mm standards, stating focal lengths in 35 mm equivalent focal length is normal in the digital camera industry.

Contents

[edit] Sensor size and aspect ratio

Drawing showing the relative sizes of sensors used in most current digital cameras.
Drawing showing the relative sizes of sensors used in most current digital cameras.

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).[2] 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".[3] 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-400, E-410 and E-420 bodies and their kit lenses, 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.)
  • 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 best dust reduction system available. (See article dust reduction system for details.)

[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 where the ISO has to be increased above 400.[4]
  • There are not as many lenses available as there are for some of the competing DSLR systems. (As mentioned above, lenses for competing systems can usually be mounted using an adaptor, but with the loss of auto-focus and with the need to manually set the aperture. Note that this is not an intrinsic disadvantage of the Four Thirds System, and the situation could change in the future. In-body image stabilization on the E-510, E-3 and E-520 can be used with non-Four Thirds System lenses.[5])
  • Telecentric optical path means more aggressive retrofocus design for wide lenses, which makes them bigger and difficult to have big apertures.

[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.
  • 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, has sensors to sell to body makers.

[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).
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.[6]

  • Olympus has announced a total of 20 lenses for the Four Thirds System, including a couple not yet released and a couple superseded by newer models. Focal lengths range from 7 to 300 mm (14–600 mm in 35 mm equivalent focal length), and include macros.[7]
  • Sigma has adapted 12 lenses for the Four Thirds System, ranging from 18 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.

[edit] References

  1. ^ "Kodak and Olympus join forces", DPReview.com, Amazon.com, 2001-02-13. Retrieved on 2007-11-07. 
  2. ^ No more compromises: The Four Thirds Standard. Olympus Europe. Retrieved on 2007-11-09.
  3. ^ Knaur Interview October 01, 2002.
  4. ^ Olympus E-3 Review, February 2008, Simon Joinson. Digital Photography Review (February, 2008). Retrieved on 2008-02-22.
  5. ^ Retro lens focus in new Olympus firmware, January 2008. Digital Photography Review (May, 2008). Retrieved on 2008-05-21.
  6. ^ Wrotniak lens list.
  7. ^ Olympus E-System Zuiko Digital Interchangeable Lens Roadmap. Olympus UK. Retrieved on 2007-11-29.

[edit] See also

[edit] External links


 

Olympus Four Thirds System Digital SLR Timeline
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Professional E-1 E-3
Midrange - Pentamirror/Prism E-500 E-510 E-520
Midrange - Porro mirror E-300 E-330
Entry-Level E-400 E-410 E-420
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