Science Fair Project Encyclopedia
In combination with variation of the lens aperture, this regulates how exposed the film will be. 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 condition, 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 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 standarised way of representing aperture so that each major aperture interval exactly doubled or halved the amount of light entering the camera (f2.8, F4, f5.6, F8, f11, f16 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:
- 1/1000 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 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 35mm photographers is that the slowest possible shutter speed that can be used with great 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. Note that using this with "great care" would normally mean bracing the camera, arms, or body to minimise camera movement. For a free-standing, unsupported photographer it is usually necessary to use the next fastest shutter speed which would be 1/125 s in this case. If a shutter speed is too slow for hand holding, a camera support—usually a tripod—must be used.
Other 35 mm handheld examples are:
- 28 mm wide angle lens, 1/30 s may be used with care, and 1/60 s is advised.
- 105 mm medium telephoto lens, 1/125 s may be used with care, and 1/250 s is advised.
- 300 mm long telephoto lens, 1/250 s may be used with care, and 1/500 s is advised.
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:
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