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Bulb (photography)
Bulb, abbreviated B, is a shutter speed setting on an adjustable camera that allows long exposure times under the direct control of the photographer. With this setting, the shutter simply stays open as long as the shutter button remains depressed. An alternative setting common on film cameras is Time, abbreviated T, where the button is pressed once to open the shutter and again to close it.
==History==
The term ''bulb'' is a reference to old-style pneumatically actuated shutters; squeezing an air bulb would open the shutter, and releasing the bulb would close it. According to the Focal Encyclopedia of Photography:〔''Focal Encyclopedia of Photography'', Frederick Purves (editor), London: Focal Press Ltd., 1956.〕
It is not clear when the term actually originated. The first industrial produced leaf shutters〔(Klaus-Eckard Riess' Homepage ''Auf und ab mit Compur'' About the history of shutters (German) )〕 from Voigtländer in Germany in 1890 had two settings: "M" for ''Moment'' exposure and "Z" for ''Zeit'' ((英語:time)) exposure. The M-setting enabled the adjustable fractions of a second.
With the Z-setting the shutter opened when pressed and closed when it was triggered again. Around 1894 the third setting "B" for ''Beliebig'' (meaning ''beliebige Zeit'', (英語:any time)) was added for the shutter of C. A. Steinheil & Söhne in Munich. The B-setting enabled his shutter to stay opened as long as the release was pressed. Bausch & Lomb in Rochester overtook these settings for their popular ''Unicum'' shutters in 1898. With the worldwide success of the shutters of Wollensak like the ''Junior'' since 1903, most of the other shutter manufacturers in the world overtook〔(T. Rand Collins MD on the Wonderful World of Vintage Camera Photography: ''Shutters'' Page about the history of leaf shutters )〕 the (now international) settings T for ''time'', I for ''instantaneous''. The B setting was kept until today for the familiar ''bulb'' behavior that could be achieved by a cable release in the English-speaking world and for ''Beliebig'' in Germany.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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