Bulb (photography)

Bulb is a shutter-speed setting on an adjustable camera that allows for long exposures under user control. When set on "B", the shutter will stay open as long as the shutter release button remains depressed. The "T", or Time, setting, on the other hand, requires one press to open the shutter and a second press 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.] ::"BULB EXPOSURE (B). Another term for a brief exposure—in which the shutter remains open only so long as the shutter release is held down. The word originated with the early pneumatic shutter release."

It is not clear when the term actually originated. It appears that when "instantaneous" shutters were introduced, they included a B setting so that the familiar "bulb" behavior could be duplicated with a cable release. This may have been the origin of the term "bulb" in reference to shutter settings. See the photo captions.

Uses

The bulb setting is usually used for exposures with a duration longer than a few seconds or even longer than the 15 second setting that is the maximum setting possible with some cameras' shutter settings.

On many digital cameras, the bulb-mode will be accessible from the LCD menu only, if possible at all. As a rule of thumb, SLR cameras do have a bulb setting and compacts do not have one. A few bridge cameras such as the Olympus SP-560UZ have a 'limited' bulb setting, allowing time exposures up till 8 minutes and at an ISO setting of 200 ISO and lower.

Because of the risk of camera movement, the camera is most often mounted on a tripod for the duration of the exposure. To further reduce the risk of camera shake, the camera's shutter is triggered by the use of a cable release or electronic remote. The cable release often has some kind of lock that can be used to keep the shutter release depressed for the duration of the exposure.

A list of picture types where the bulb setting is useful:
* Photographing fireworks at night
* Photographing the night sky and celestial objects.
* Photographing lightning
* Photographing streets at night (where the streaks from moving cars lights can be seen, not the cars)

References