Four thirds
Four Thirds is a standard for a digital camera system developed by Olympus and Kodak . Right from the start, no consideration was given to conventional lenses , cameras or sensor sizes. This made it possible to avoid compatibility problems with old components as well as compromises in the design of the new components. The first such camera, the Olympus E-1 , was presented in autumn 2003.
The standard defines, among other things, the sensor dimensions, the lens bayonet including the communication protocol, the imaging circle and the flange focal length (38.85 mm), but also optical requirements such as the maximum angle between light beams hitting the sensor.
The production of the last Four Thirds components was discontinued in 2017 in favor of the Micro Four Thirds standard, available since 2008, with the same sensor size but different lens geometry.
Origin of name
The name of the standard derives from the external dimensions of the sensor (not its effective image diagonal), defined according to the traditional measuring method of the nominal size of image sensors based on the size of the corresponding vacuum image recording tube, specified as the diameter of the corresponding tube in inches .
In the case of a Four Thirds image sensor, the image size corresponds to the size of the image which can be displayed on the light-sensitive surface of an image recording tube with an outer diameter of four thirds of an inch . Typically, the diagonal of the usable sensor surface was around two thirds of the outer diameter in such tubes, which explains the sensor diagonal of just under 22 millimeters. The naming Four Thirds has nothing to do with the aspect ratio 4: 3 .
Sensor size
The image diagonal of Four Thirds sensors is standardized (with the Micro Four Thirds standard it was adopted and not changed). At 21.633 mm, it is exactly half the diagonal of the 35mm format (43.267 mm), which corresponds to a format factor of 2.0. Lenses with focal lengths between 20 and 25 mm are therefore normal lenses for this format .
Most cameras have a sensor with an aspect ratio of 4: 3 and an optically effective area of 17.31 mm × 12.98 mm (area 224.64 mm²).
The Panasonic DMC-GH1 and DMC-GH2 have an oversized multi-aspect sensor ( multi-format sensor ) measuring 18.89 mm × 14.48 mm. This enables the use of the largest possible diagonal for these aspect ratios:
| format | pixel | MP | Width × height |
|---|---|---|---|
| 4: 3 | 4608 × 3456 | 15.92 | 17.31 mm x 12.98 mm |
| 3: 2 | 4752 × 3168 | 15.05 | 17.85 mm x 11.90 mm |
| 16: 9 | 4976 × 2800 | 13.93 | 18.69 mm x 10.52 mm |
Licensee
Due to an open licensing policy, every manufacturer is free to bring standard accessories for the system onto the market. Compatible components from different manufacturers can thus be combined with one another.
The first product available on the market was in 2003, when, besides Olympus, only the two providers Fujifilm and Kodak supported the new standard, the Olympus E-1 . In 2004 three more companies were added: Panasonic , Sanyo and Sigma . The following other manufacturers officially support the standard: Astrodesign , Cosina , Leica Camera , Carl Zeiss , Schneider-Kreuznach , Tamron and Tokina .
Further development
At the beginning of August 2008, Panasonic and Olympus presented the so-called Micro-Four-Thirds standard as a further development of the four-thirds system standard , with which compact camera systems with interchangeable lenses are possible. The new standard uses a smaller flange focal length and a narrower bayonet connection, which makes it practically impossible to use with SLR cameras .
With a mechanical adapter and because of the electronic compatibility, however, it is possible to continue using lenses of the Four Thirds standard, although the Micro Four Thirds standard with eleven electrical contacts has two additional contacts intended for video applications. Olympus discontinued the production of Four Thirds lenses in 2017.
important characteristics
Requirements for the lenses
Lenses of the Four Thirds standard basically have the system's bayonet . There are also limit values for the fanning out of the light beam emerging from the lens. This should be as parallel as possible, since digital image sensors (in contrast to chemical film) develop their full sensitivity only when light hits perpendicularly (see also telecentrics ). The image circle required in the standard is relatively large in relation to the sensor size in order to achieve uniform illumination of the sensor. These requirements seem particularly at wide angle lenses and open aperture of vignetting counter the image.
As with most digital cameras, the sensor size differs from the dimensions of 35mm film , which is used as a reference because of its once widespread use. Due to its smaller size, there is an apparent doubling of the focal length with regard to the image section.
Due to the required smaller imaging area, bright lenses also have smaller dimensions, which is noticeable through their lower weight.
Depth of field
The depth of field of a four-thirds lens on a four-thirds sensor is about twice as large as with sensors with the same size as 35 mm images, with the same f-number and the same perspective and the same image section. More precisely, the depth of field and the diffraction blur of a telescopic Four Thirds lens with a focal length of 150 millimeters at an aperture of 2.8 correspond exactly to those of a 35mm lens on a 35mm sensor with a focal length of 300 millimeters at an aperture of 5.6.
To a the small picture format appropriate depth of objects or people against a diffuse background with Four Thirds indemnify , you have to with this sensor format fade in two stages. A four-thirds lens therefore images the area sharply at a f-number of 2 that a 35-mm lens images sharply at a f-number of 4.
The greater depth of field of the Four Thirds format is always advantageous when several people or objects are to be photographed that are not on the same level of focus (for example a group photo in several rows), when the background is also to be sharp or when a subject moves towards or away from the camera when recording moving images. The gain in depth of field is also desirable in macro photography, since the closer you get to the object, the depth of field also decreases.
Noise floor and dynamic resolution
The signal level of an (ideal) sensor element is proportional to the amount of incident light. With a smaller image sensor, the dynamic resolution is lower for the same number of image points, since the amount of light per image point is reduced if the same image angle and the same aperture number are used. During the necessary amplification, undesired thermal noise is also amplified, which means that smaller sensors tend to show a poorer signal-to-noise ratio . If, with the same number of pixels and the same angle of view, the same aperture width is used instead of the same f-number , each pixel receives the same amount of light, which results in a comparable signal and noise behavior.
With the same aperture, half the image size and half the focal length, a lens differs mainly in its shorter design and the resulting lower volume and weight. In particular, the depth of field of the image and the image angle as well as the luminous flux and thus the light sensitivity per pixel are identical.
The Four Thirds sensor is currently the smallest among the SLR cameras. The competing SLR cameras with APS-C sensors have sensors with around 56 percent (Canon EF-S) and 78 percent (Nikon DX, Pentax, Sony DT) more area. Sensors in 35 mm format are about four times the size. Compared to the sensors in most compact cameras, however, a four-thirds chip still has an area around 5 ( 1 ⁄ 1.7 ″ sensors) to 16 times ( 1 ⁄ 3 ″ sensors) as large.
If a motif of a certain brightness is imaged at a given angle, a lens focal length that is around 20 percent shorter is necessary with Four Thirds than, for example, with a camera with an APS-C sensor. If you compare corresponding lenses with the same f-number, the actual aperture in the case of Four Thirds is 20 percent smaller, which corresponds to a reduction in the amount of incident light by around a third. This results in a dynamic resolution that is reduced by around 30 percent, combined with an increase in the noise floor of around 50 percent. It should be noted that in this estimate, differences in the image sensor technology between the camera systems were not taken into account (the actual differences in performance between two specific camera models can therefore be noticeably smaller or sometimes significantly larger).
In practice, the reduced dynamic resolution usually plays a subordinate role, as the values achieved are still outside of what a printout or a JPEG image can reproduce. However, the increased background noise is annoying if no flash is to be used in a dark environment and a high ISO setting, i.e. a high gain, has to be used instead. In addition, it can be important in shooting situations in which areas in subjects with very large image dynamics (actually underexposed) are to be post-processed and brightened with the help of the stored raw data .
Communication between camera and accessories
A central feature of the system are intelligent components that communicate with each other via electrical contacts using a protocol that is also defined in the standard.
In this way, focus data, aperture selection and focal length are electronically transmitted between the camera and lens as in competing systems. The Four Thirds system can also transfer lens characteristics such as distortion or vignetting characteristics to the camera, which enables imaging errors to be compensated digitally.
Backward Compatibility
Since Four Thirds is a new development, there is initially no complete downward compatibility with other systems. In addition, the previous OM system from the manufacturer Olympus used a purely mechanical bayonet without automatic focusing or aperture control, so there was no need to consider compatibility. OM lenses can be operated with an adapter ring on the Four Thirds bayonet. This also applies to a number of other non-system lenses.
Camera body
Models of the Four Thirds Standard presented so far in the order of their presentation to the public are:
| 2003 | 2004 | 2005 | 2006 | 2007 | 2008 | 2009 | 2010 |
|---|---|---|---|---|---|---|---|
| E-1 a | E-300 | E-500 | E-330 b, e | E-410 b | E-420 b | E-620 b, c, f | E-5 a, b, c, f |
| Panasonic Lumix DMC-L1 b, d | E-510 b, c | E-520 b, c | E-450 b | ||||
| Leica Digilux 3 b, d | Panasonic Lumix DMC-L10 b, d, f | E-30 b, c, f | |||||
| E-400 | E-3 a, b, c, f |
Lenses
| Wide angle zoom | Standard zoom | Telephoto zoom | macro | Fixed focal length | Teleconverters and adapters |
|---|---|---|---|---|---|
| Olympus 7-14mm f / 4.0 | Olympus 12-60mm f / 2.8-4.0 SWD | Olympus 35-100mm f / 2.0 | Olympus 35mm macro f / 3.5 | Olympus 8mm f / 3.5 fisheye | Olympus EC-14 1.4 × teleconverter |
| Olympus 9-18mm f / 4.0-5.6 | Olympus 14-35mm f / 2.0 SWD | Olympus 40-150mm f / 4.0-5.6 | Olympus 50mm macro f / 2.0 | Sigma 24mm f / 1.8 macro | Olympus EC-20 2.0 × teleconverter |
| Sigma 10-20 mm f / 4.0-5.6 HSM | Olympus 14-42 mm f / 3.5-5.6 | Olympus 50-200mm f / 2.8-3.5 SWD | Sigma 105mm f / 2.8 macro | Leica 25mm f / 1.4 | Olympus EX-25 Extension Tube |
| Olympus 11-22mm f / 2.8-3.5 | Leica 14–50 mm f / 2.8–3.5 OIS | Sigma 50-500 mm f / 4.0-6.3 HSM | Sigma 150mm f / 2.8 HSM | Olympus 25mm f / 2.8 pancake | Olympus MF-1 OM system adapter |
| Leica 14–50 mm f / 3.8–5.6 OIS | Sigma 55-200 mm f / 4.0-5.6 | Sigma 30mm f / 1.4 HSM | |||
| Olympus 14-54 mm f / 2.8-3.5 | Sigma 70-200 mm f / 2.8 HSM ?? | Sigma 50mm F1.4 EX DG HSM | |||
| Leica 14–150 mm f / 3.5–5.6 OIS | Olympus 70-300mm f / 4.0-5.6 | Olympus 150mm f / 2.0 | |||
| Sigma 18-50mm f / 2.8 macro | Olympus 90-250mm f / 2.8 | Olympus 300mm f / 2.8 | |||
| Sigma 18-50 mm f / 3.5-5.6 | Sigma 300-800 mm f / 5.6 HSM | ||||
| Olympus 18-180mm f / 3.5-6.3 |
Explanation : SWD / HSM = lens with ultrasonic drive , OIS = lens with optical image stabilizer
literature
- Late Frank: Olympus E-System. November 2003, ISBN 3-925334-65-3 .
Web links
Individual evidence
- ↑ a b Richard Butler: In memoriam: Olympus brings down the curtain on the legacy Four Thirds system , dpreview.com of March 10, 2017, accessed on March 15, 2017.
- ↑ A peculiarity in specifying the size of a video tube still determines the size of CCD sensors in digital cameras : See Vidicon # size specification
- ↑ Test report on the Panasonic LUMIX DMC-GH1 at dpreview.com (English), accessed on August 13, 2009.
- ↑ Test report about the Panasonic LUMIX DMC-GH2 at dpreview.com (English)
- ↑ Information for the DMC-GH2
- ↑ Digital SLR camera Olympus E-1 - Sharp Perspektiven , test.de , accessed online on October 1, 2012.
- ↑ FourThirds finds trailers , test.de , accessed online on October 1, 2012
- ↑ a b Kenko Tokina, Tamron, and Astrodesign join the Micro Four-Thirds standard , accessed online January 27, 2012
- ↑ Tamron joins the Micro Four Thirds Standard ( Memento June 30, 2012 in the Internet Archive ), accessed online on January 27, 2012.
- ↑ a b c Effect of image size on imaging parameters, Wikibook digital imaging methods. Chapter Image Acquisition , accessed June 24, 2015
- ↑ Digital imaging methods: image recording - Wikibooks, collection of free textbooks, non-fiction and specialist books. In: de.wikibooks.org. Retrieved January 12, 2017 .
- ↑ Zuiko Digital ED 14-35mm, F2.0 SWD. (No longer available online.) Archived from the original on September 29, 2017 ; accessed on June 6, 2017 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ Zuiko Digital ED 14-35mm, F2.0 SWD. Retrieved June 6, 2017 .
