Bulb

Abbreviated B, is a shutter speed setting on an adjustable camera that allows for long exposure times under the direct control of the photographer. With this setting, the shutter 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.

The bulb setting is used on some cameras, including some point-and-shoot cameras, to obtain shutter speeds slower than the maximum offered by the camera otherwise.

Because of the risk of camera movement, the camera is most often mounted on a tripod for the duration of the exposure. While it's generally possible to use the shutter release button on the camera itself, a cable release or electronic remote is often used to further eliminate the risk of shaking the camera during the long exposure. The cable releases generally include a locking feature to eliminate the need to keep the button or plunger depressed during extremely long exposures.

The bulb setting is useful for the following types of photographic subjects:

• fireworks at night
• the night sky and celestial objects
• lightning
• streets at night (creating streaks from moving cars)

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