Bulb Mode
A shutter setting, marked B, that keeps the shutter open for as long as the release is held down.
Measured in
seconds
In depth
Bulb takes over where the camera's longest timed speed ends, usually thirty seconds, and it is indispensable for star trails, light painting and long-exposure landscape work. It demands a locking cable release or intervalometer, since holding the button by hand introduces vibration and makes accurate timing impossible.
Examples in practice
A four-minute bulb exposure at f/8 turns a breaking sea into smooth mist and stretches cloud into streaks.