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. Al ...

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 conceptual material accepted as official in a fictional universe by its fan base * Literary canon, an accepted body of works considered as high culture ** Western ca ...

Fuji Fuji may refer to: Places China * Fuji, Xiangcheng City (付集镇), town in Xiangcheng City, Henan Japan * Mount Fuji, the tallest mountain in Japan * Fuji River * Fuji, Saga, town in Saga Prefecture * Fuji, Shizuoka, city in Shizuoka Prefec ...

, Hitachi, Ikegami, JVC, Matsushita (Panasonic),

Nikon (, ; ), also known just as Nikon, is a Japanese multinational corporation headquartered in Tokyo, Japan, specializing in optics and imaging products. The companies held by Nikon form the Nikon Group. Nikon's products include cameras, camera ...

Sony , commonly stylized as SONY, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan. As a major technology company, it operates as one of the world's largest manufacturers of consumer and professiona ...

and

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. 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 standardization organization in Japan. ARIB is designated as the center of promotion of the efficient use of the radio spectrum and designated frequency change support agency. Its activities include those previously ...

, 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 and spherochromatism, is a failure of a lens to focus all colors to the same point. It is caused by dispersion: the refractive index of the lens elements varies with the w ...

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 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, SD, often shortened to standard definition) is a television system which uses a resolution that is not considered to be either high or enhanced definition. "Standard" refers to it being the prevailing sp ...

was captured at 4:3 aspect ratio. Nowadays, cameras with the same mount capture HD with 16:9 aspect ratio, 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 Digital photography