A technique for shooting photos by leaving the lens open longer than normal
Typically several seconds. The shutter on the camera is most often operated in the manual mode and left open the entire time the shutter release button is pressed. Consequently, the camera is able to acquire images not readily available to the naked eye (things such as streaks left by auto headlights, in place of the cars themselves).
Bulb, simply abbreviated as B, is a setting for shutter speed on an automatic camera allowing for long exposure periods directly controlled by the photographer. Using this function, the shutter simply remains open for the length of time the shutter button remains in a depressed state. An alternative choice typical on other film cameras is just Time, abbreviated as T, where pressing the button once for opening the shutter and once more to close it
The "bulb" term was coined for the old-style pneumatically triggered shutters; by squeezing a bulb with air the shutter would open and letting go of the bulb closed it.
The length of a night exposure causes the lights on moving cars to streak across
a highway image at night
It seems that when the instantaneous shutters were created, they incorporated a B setting allowing the customary bulb behavior to be replicated using a cable release.
The bulb function is most often used for exposures lasting longer than a just few seconds or for exposures longer than the maximum 15 second settings on some cameras.
1898 Bausch & Lomb advertisement showing a Unicom Shutter with B setting; the explanation displayed "bulb exposure" in quotation marks and explained it in detail, since the term was still novel.
The Unicom Shutter is of the same general form
as the iris diaphragm shutter and is intended to meet the demand for a
cheaper, yet well made and durable shutter. The case of the Unicom
Shutter is of highly finished bronze metal and the actuating mechanism is
protected from dust and injury. The shorter blades are of thin rubber so
shaped as to give the most even illumination possible with two blades only,
the aperture formed by them at first being elliptical, becoming circular.
Back of the shutter blades, there is an iris diaphragm operated by the index
lever at the lower margin of the shutter by which the desired size of the
stop can be obtained.
The shutter gives automatic exposures from one hundredth of a second to
one second and has in addition a "bulb exposure" so arranged that
compression of the pneumatic bulb opens the shutter and the blades remain
open as long as the bulb is compressed, closing instantly when it is
released. This is a very useful feature as short exposures over one second
can be made with sufficient accuracy and in photographing children, animals
and other objects where their movements are uncertain. it is also possible
to obtain a much longer exposure with the bulb than it would be save to
hazard with the automatic exposure. The shutter also has regular time
exposure, the blades being opened by the pressure of the bulb and remaining
open until closed again by the bulb
Many digital cameras now have the bulb-mode available only from their LCD menu, if a bulb setting exists at. A general rule of thumb, is that DSLR cameras contain a bulb setting while compact cameras do not. Although a small number of bridge cameras like the
Canon PowerShot SX40 HS feature a bulb setting that's 'limited',
while other cameras may provide for time exposures as long as 8 minutes using an ISO of 200 ISO or lower.
Due to great risk of the camera moving, it's typically mounted upon a tripod during the entire exposure time. To further diminish any possibility of the camera shaking, the camera shutter is actuated by using an electronic remote or a mechanical cable release. The cable release typically features some sort lock that can carry out keeping the shutter release open for the length of the exposure.
Oct 9, 2011
A list of types of photographs where a bulb setting is helpful: