Bulb Mode: Exposures Longer Than 30 Seconds

Bulb Mode: Exposures Longer Than 30 Seconds

Most cameras have a maximum shutter speed of 30 seconds in normal modes. For exposures longer than that, you need bulb mode. In bulb mode, the shutter stays open as long as you hold the shutter button down. With a remote shutter release that has a lock function, you can hold the shutter open for minutes or even hours. Bulb mode is essential for night photography, star trails, light painting, and any situation where you need an exposure longer than 30 seconds.

Using bulb mode requires a few pieces of equipment. A remote shutter release with a lock or intervalometer function lets you open the shutter and walk away. A fully charged battery is important because long exposures drain battery power. Long exposures also generate heat in the sensor, which increases noise. Many cameras have long exposure noise reduction that takes a second dark frame exposure after the main exposure and subtracts the noise pattern, but this doubles the time for each shot.

Calculating exposure in bulb mode requires experimentation. The camera's light meter may not work in very dark conditions. Start with a test exposure and check the histogram. For star photography, a common starting point is 20 to 30 seconds at f2.8 with ISO 3200 or 6400. For star trails, you want much longer exposures, 15 minutes to several hours, at a lower ISO like 400 or 800 with a narrower aperture. Light painting might require a few minutes at a mid-range aperture and low ISO.

Sensor noise becomes more noticeable in long exposures. Hot pixels, which are individual pixels that appear bright in long exposures, become more visible. The camera's long exposure noise reduction feature handles this by capturing a dark frame that maps the hot pixels and subtracts them. However, this doubles the shooting time. An alternative is to take a few dark frames separately and use software to subtract the noise in post-processing. This lets you shoot more frames in the field.

Bulb mode is also used for light painting, where you move a light source through the frame during the exposure to paint shapes or illuminate specific objects. The long exposure captures the light trail of the moving source. Multiple light sources, colored gels, and different movement patterns create endless creative possibilities. Light painting works best in complete darkness with a controlled light source and careful planning of the light's path.