Shutter speed

In photography, shutter speed is the time for which the shutter is held open during the taking of a photograph to allow light to reach the film or imaging sensor (in a digital camera).

In combination with variation of the lens aperture, and film/sensor sensitivity, this regulates how exposed how much light the camera will record. For a given exposure, a fast shutter speed demands a larger aperture to avoid under-exposure, just as a slow shutter speed is offset by a very small aperture to avoid over-exposure. Long shutter speeds are often used in low light conditions, such as at night.

Shutter speed is measured in seconds. A typical shutter speed for photographs taken in sunlight is 1/125th of a second. In addition to its effect on exposure, shutter speed changes the way movement appears in the picture. Very short shutter speeds are used to freeze fast-moving subjects, for example at sporting events. Very long shutter speeds are used to intentionally blur a moving subject for artistic effect.

In early days of photography, available shutter speeds were somewhat ad hoc. Following the adoption of a standardized way of representing aperture so that each major aperture interval exactly doubled or halved the amount of light entering the camera (f/2.8, f/4, f/5.6, f/8, f/11, f/16 etc.), a standardized 2:1 scale was adopted for shutter speed so that opening one aperture stop and reducing the shutter speed by one step resulted in the identical exposure. The agreed standard for shutter speeds is:

1/8000 s
1/4000 s
1/2000 s
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 (for bulb) — keep the shutter open as long as the release lever is engaged.
T — keep the shutter open until the lever is pressed again.

This scale can be extended at either end in specialist cameras.

The term "speed" is improperly used, except if we speak of the inverse of the "exposure time". "Exposure time" is measured in seconds and "shutter speed" in terms of the inverse of a second, which is an appropriate measure of “speed”. So we would have the following "speed" measures:

8000 s^-1
4000 s^-1
2000 s^-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
1 s^-1

The ability of the photographer to take images without noticeable blurring by camera movement is an important parameter in the choice of slowest possible shutter speed for a handheld camera. The rough guide used by most 35 mm photographers is that the slowest possible shutter speed that can be used with care is the shutter speed numerically closest to the lens focal length. For example, for handheld use of a 35 mm camera with a 50 mm normal lens, the closest shutter speed is 1/60 s. The rule can be a augmented with knowledge of the intended application for the photograph, an image intended for significant enlargement and closeup viewing would require faster shutter speeds to avoid obvious blur. Through practice and special techniques such as bracing the camera, arms, or body to minimize camera movement longer shutter speeds can be used without blur. If a shutter speed is too slow for hand holding, a camera support—usually a tripod—must be used. There are also stabilized lenses available.

Cinematographic Shutter Formulae

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 a standard 24 frame/s.

Where E = Exposure, F = Frames per second, and S = Shutter opening:

E = \frac {F*360^\circ}{S}

S = \frac {F*360^\circ}{E}

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Cinematographic Shutter Formulae

See also