Definition: Bulb Mode; Bulb Setting

Bulb mode | Glossary entry

Bulb Mode; bulb Setting

The ‘B’ setting on the camera ‘modes’ dial stands for ‘Bulb’. On some old film cameras the ‘B’ setting is sometimes known as ‘T’ for time. The bulb mode setting is a shutter speed setting. Digital cameras normally have maximum shutter speed settings up to 30 seconds. For exposures longer than 30 secs you will need to use ‘bulb mode’.

Bulb mode is only found on an adjustable camera. It is a full manual setting. In some very old film cameras the shutter was opened by squeezing an air bulb. Air actuated the shutter while the bulb was squeezed. On releasing it the shutter closed. The name has stuck. In post-war SLRs ‘bulb mode’ was activated by holding down the shutter button until the exposure was complete. On release of the button the shutter closed. The exposure was then complete.

Activating ‘bulb mode’

‘B’ or bulb mode on a DSLR is activated by one of three methods. These depend on the make and model of the camera…

  • Press and release the shutter release button. To complete the exposure the button is pressed again. Then the shutter closes. Most cameras using this method have an auto-closer to time-out the shutter after a default time. So if the shutter button is not pressed again it will close the shutter automatically after, say, 30 minutes.
  • Press and hold the shutter release button for the duration of the exposure. On release of the button the shutter closes. Pressing the shutter button by hand for long exposures will move the camera. Use a tripod.
  • Most cameras can also have the bulb mode activated by electronic remote control. These generally allow for the “press, exposure, press-again” method of shutter control. Remote control minimises movement as you are not touching the camera. When using remote controls Follow the instructions in the manual.

Very long exposures using the bulb mode setting allow a range of photograph types that are not normally available on other settings. For example…
Fireworks, light trails, star trails, moving vehicles at night, lighted streets and buildings at night.

Bulb mode is found on most DSLRs, but may not be found on bridge cameras or point and shoot cameras and some other older, cheap popular cameras.

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Damon Guy (Netkonnexion)

Damon is a writer-photographer and editor of this site. He has also run some major websites, a computing department and a digital image library. He started out as a trained teacher and now runs training for digital photogs.
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