The B4 lens mount was standardized in 1992 by the Broadcasting Technology Association (BTA) and is defined in BTA S-1005. This standard defines the physical mount, but also optical properties and some electrical connections. The B4 mount defines the sensor to have a diagonal size of 11 mm (a so-called 2/3" size sensor). The B4-mount is used by practically all 2/3" broadcast lenses and cameras (as of 2019). Although the standard was set in 1992, the B4 mount already existed before 1980. The Sony BVP-300, produced from 1978, was possibly the first camera with a B4 mount. Further, all Sony

Betacam Betacam is a family of half-inch professional videocassette products developed by Sony in 1982. In colloquial use, ''Betacam'' singly is often used to refer to a Betacam camcorder, a Betacam tape, a Betacam video recorder or the format itself. ...

cameras had a B4 mount. The BTA was formed by Japanese broadcaster NHK and included members from

Canon Canon or Canons may refer to: Arts and entertainment * Canon (fiction), the material accepted as officially written by an author or an ascribed author * Literary canon, an accepted body of works considered as high culture ** Western canon, th ...

, Fuji,

Hitachi () is a Japanese Multinational corporation, multinational Conglomerate (company), conglomerate founded in 1910 and headquartered in Chiyoda, Tokyo. The company is active in various industries, including digital systems, power and renewable ener ...

, Ikegami,

JVC JVC (short for Japan Victor Company) is a Japanese brand owned by JVCKenwood. Founded in 1927 as the Victor Talking Machine Company of Japan and later as , the company was best known for introducing Japan's first televisions and for developin ...

, Matsushita (Panasonic),

Nikon (, ; ) is a Japanese optics and photographic equipment manufacturer. Nikon's products include cameras, camera lenses, binoculars, microscopes, ophthalmic lenses, measurement instruments, rifle scopes, spotting scopes, and equipment related to S ...

Sony is a Japanese multinational conglomerate (company), conglomerate headquartered at Sony City in Minato, Tokyo, Japan. The Sony Group encompasses various businesses, including Sony Corporation (electronics), Sony Semiconductor Solutions (i ...

and

Toshiba is a Japanese multinational electronics company headquartered in Minato, Tokyo. Its diversified products and services include power, industrial and social infrastructure systems, elevators and escalators, electronic components, semiconductors ...

. It was formed in the mid-1980s and set various standards for television. It is now part of

ARIB The , commonly known as , is a Standards organization, standardization organization in Japan. ARIB is designated as the center for promotion of the efficient use of the radio spectrum and the designated frequency change support agency. Its activit ...

, Association of Radio Industries and Businesses.

Mechanical

The flange of the mount defines the positioning of the lens relative to the image sensor. A ring is present around the opening on the camera which, when rotated, tightly locks the flange of the lens against the camera. A pin on the top side of the lens flange and a hole in the camera mount make sure the lens cannot be mounted at an angle.

Optical

The B4-mount has its image projected at 48 mm behind the lens mount flange (in air). The standard defines that a prism splits the light to form separate images planes for the colours red, green and blue. A correction for

chromatic aberration In optics, chromatic aberration (CA), also called chromatic distortion, color aberration, color fringing, or purple fringing, is a failure of a lens to focus all colors to the same point. It is caused by dispersion: the refractive index of the ...

is also part of the standard: the red sensor should be 10 μm further, and the blue one 5 μm further than 48 mm. This fitted well with established TV-camera technology using 3 tubes, and also with

3CCD A three-CCD (3CCD) camera is a camera whose imaging system uses three separate charge-coupled devices (CCDs), each one receiving filtered red, green, or blue color ranges. Light coming in from the lens is split by a beam-splitter prism into ...

, a technology in development at the time of the definition of the standard. The standard defines that the diagonal size of the projected image should be 11 mm, but does not define a resolution to be used. In the past

standard definition Standard-definition television (SDTV; also standard definition or SD) is a television system that uses a resolution that is not considered to be either high or enhanced definition. ''Standard'' refers to offering a similar resolution to the ...

was captured at 4:3

aspect ratio The aspect ratio of a geometry, geometric shape is the ratio of its sizes in different dimensions. For example, the aspect ratio of a rectangle is the ratio of its longer side to its shorter side—the ratio of width to height, when the rectangl ...

. Nowadays, cameras with the same mount capture HD with 16:9

, or even 4K video, thanks to improved lenses.

Electrical

The lens mount is accompanied by a connector for the electrical connections. It powers the lens motors, controls the iris and allows a few buttons on the lens handle to control camera functions. The connectors are made by Hirose. On the camera is a HR10-10R-12S receptacle, and on the lens a cable with a HR10-10P-12P plug.Fujinon A13x4.5BERD-S48 operation manual, p.38, Fuji Photo Optical Co., ltd., document number LP150D-S48 1409

References

{{reflist Lens mounts