Bulb.
1. A glass shell containing a metal filament or gaseous vapours. Such bulbs - tungsten lamps, tungsten halogen lamps, fluorescent lamps, flash tubes - can produce light.
cf. flash unit, fluorescent lamp, halogen, tungsten.
2. An exposure setting which leaves the shutter open for as long as you keep the shutter release pressed down. Marked as “B” or “bulb” on many cameras.
This setting is very useful, therefore, for fully manual long exposure photographs - typically over 30 seconds or so. Many cameras support external cable releases, which let you take bulb photos without the risk of bumping the camera accidentally and blurring the photo. Many such cables have a locking ring, so you can open the shutter, lock it in place and walk away for the duration of the shot.
Many computerized cameras have wired shutter releases with locking electrical switches which behave in a similar fashion. Others have wireless shutter releases which let you take bulb photos by pressing the wireless controller once to open the shutter and once to close it. (like the old T mode)
The name “bulb” comes from the days of mechanical-camera photography when really long cable releases consisted of a hose and a spherical pneumatic rubber bulb which the photographer would squeeze to trigger the shutter. (the air pressure change would push down the button)
Entry last updated 2002-04-03. Term 166 of 1487.
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