Bulb (photography)

[3] Though mechanically timed exposures could also be triggered by squeezing the shutter release bulb, "Bulb" exposures then had the same momentary action as camera shutters have today, as per this description from Sears Roebuck's 1909 Cameras [&] Photographic Supplies: With the indicator set to B, the shutter opens when the bulb is pressed and remains open as long as the pressure is maintained (“bulb” exposure), a very convenient means of making time exposures of only a few seconds’ duration.Around 1894 in Germany, the momentary-action setting on camera shutters made by C. A. Steinheil & Söhne in Munich were denoted with "B" but the literature referred to it as Beliebig (meaning beliebige Zeit, English: "Any time").

The Eastman Kodak Company sold entry level consumer cameras that did not have the option of a pneumatic shutter release.

The cable releases generally include a locking feature to eliminate the need to keep the button or plunger depressed during extremely long exposures.

[5] In 2012, Olympus introduced a new form of bulb mode with their "Live Bulb" (without toggle) and "Live Time" (with toggle) settings in their Olympus OM-D E-M5 digital camera, where the viewfinder and display gets updated during the exposure in order to allow the photographer to inspect the exposure while it "develops".

The display refresh rate for this mode can be configured between 0.5 s and 60 s. Some specialized cameras use other image triggers.

Bulb is named for the bulb on detachable rubber pneumatic shutter releases that came with early cameras. With shutters set to "B", the pneumatic release kept the shutter open for as long as the photographer squeezed the bulb—a "Bulb" exposure.
This 30-second exposure shows the flight trails of several insects around a floodlight at night.