Shutter speed

In photography the time which the shutter is held open during the taking of a photograph to allow light to reach the film.

In combination with variation of the lens aperture, this will regulate how exposed the film will be. A fast shutter speed will demand a larger aperture to avoid under-exposure, just as a slow shutter speed will be offset by a very small aperture to avoid over-exposure.

Shutter speed is measured in seconds. A typical shutter speed for photographs taken in sunlight is 1/125th of a second. Very short shutter speeds are used to freeze fast-moving subjects, for example at sporting events. Very long shutter speeds are used in low-light conditions such as night or to intentionally blur a moving subject for artistic effect.

In early days of photography, available shutter speeds were somewhat ad hoc, but later a standardised 2:1 scale was adopted, which can be extended at either end:

• 1/1000 s
• 1/500 s
• 1/250 s
• 1/125 s
• 1/60 s
• 1/30 s
• 1/15 s
• 1/8 s
• 1/4 s
• 1/2 s
• 1 s
• B -- keep the shutter open as long as the release lever is engaged.
• T -- keep the shutter open until the lever is pressed again.

In cinematography, shutter speed is a function of the frame rate and shutter angle. Most motion picture film cameras use a rotating shutter with a shutter angle of 170° to 180°, which leaves the film exposed for about 1/48 or 1/50 second at standard 24 fps speed.

See also: Exposure, shutter