Bulb, abbreviated B, is a setting on an adjustable camera that allows for long exposure times under the direct control of the photographer. With this setting, the simply stays open as long as the shutter release 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: It is not clear when the term actually originated. The first industrial produced leaf shutters from in Germany in 1890 had two settings. 'M' for Moment exposure and 'Z' for Zeit (Engl.: ...