Bulb Mode is an exposure setting that is used when seeking to use a shutter speed
of more than 30 seconds. Generally, this would be used in extremely low light situations, such as taking photos of the night sky.
To use Bulb mode – accessed by turning the shooting mode dial to B on some EOS cameras
, and as a shutter speed setting in M
on others - you hold down the shutter button for as long as you want the shutter to remain open. To really make Bulb shooting work for you, you need to use a sturdy tripod, and ideally a remote shutter release, both of which will prevent the camera from moving during exposure.
So why use Bulb mode? You use Bulb mode in instances where you want to use shutter speeds greater than 30 seconds (the maximum selectable speed in TV
and M, or to expose for the duration of something happening in your scene, such as a firework going off. It’s also the mode you would use for start trails photography.