Shutter speed

In photography, shutter speed refers to 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.

The ability of the photographer to take images without noticeable blurring by camera movement is an important parameter in the choice of shutter speed. For handheld use with a normal lens, shutter speeds above 1/60 s are considered safe, and 1/60 s can be used with care. For wide angle lenses, 1/30 s may be used with care, whereas telephoto lenses require shorter shutter speeds proportionally so according to their focal lengths.

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, f number