Bulb mode allows you to keep the camera shutter open for as long as you keep the shutter button depressed. Many cameras represent it with the letter B on the shutter speed scale. Bulb mode is essential in night-time photography, or if you are trying to shoot special effects (e.g. star trails).

Most SLRs and an increasing number of compact digital cameras feature a bulb mode.

Due to camera shake, you need to place your camera on a tripod or a (flat surface) if you are going to use bulb mode. You probably also ought to use a cable release or remote control and consider using mirror lock-up, if your camera has that facility.