In photography, shutter speed or exposure time is the length of time a camera's shutter is open when taking a photograph. The amount of light that reaches the film or image sensor is proportional to the exposure time.
The camera's shutter speed, the lens's brightness (f-number), and the scene's luminance together determine the amount of light that reaches the film or sensor (the exposure). Exposure value (EV) is a single quantity that accounts for the shutter speed and the f-number.
Multiple combinations of shutter speed and f-number can give the same exposure value. Doubling the exposure time doubles the amount of light (subtracts 1 EV). Making the f-number one stop brighter (reducing the f-number by a factor of ) also doubles the amount of light. A shutter speed of 1/50 s with an f/4.0 lens gives the same exposure value as a 1/100 s shutter with an f/2.8 lens, and also the same exposure value as a 1/200 s shutter with an f/2.0 lens.
In addition to its effect on exposure, the shutter speed changes the way movement appears in photographs. Very short shutter speeds can be 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. Short exposure times are sometimes called "fast", and long exposure times "slow".
Adjustment to the aperture controls the depth of field, the distance range over which objects are acceptably sharp; such adjustments need to be compensated by changes in the shutter speed.
In early days of photography, available shutter speeds were not standardized, though a typical sequence might have been 1/10 s, 1/25 s, 1/50 s, 1/100 s, 1/200 s and 1/500 s. Following the adoption of a standardized way of representing aperture so that each major step 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 standards for shutter speeds are:
With this scale, each increment roughly doubles the amount of light (longer time) or halves it (shorter time).
Camera shutters often include one or two other settings for making very long exposures:
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 shutter speed that can be used easily without much blur due to camera shake 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. This rule can be 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. Image stabilization can often permit the use of shutter speeds 3–4 stops slower (exposures 8–16 times longer).
Shutter priority refers to a shooting mode used in semi-automatic cameras. It allows the photographer to choose a shutter speed setting and allow the camera to decide the correct aperture. This is sometimes referred to as Shutter Speed Priority Auto Exposure, or TV (time value) mode.
Shutter speed is one of several methods used to control the amount of light recorded by the camera's digital sensor or film. It is also used to manipulate the visual effects of the final image beyond its luminosity.
Slower shutter speeds are often selected to suggest movement in a still photograph of a moving subject.
Excessively fast shutter speeds can cause a moving subject to appear unnaturally frozen. For instance, a running person may be caught with both feet in the air with all indication of movement lost in the frozen moment.
When a slower shutter speed is selected, a longer time passes from the moment the shutter opens till the moment it closes. More time is available for movement in the subject to be recorded by the camera.
A slightly slower shutter speed will allow the photographer to introduce an element of blur, either in the subject, where, in our example, the feet, which are the fastest moving element in the frame, might be blurred while the rest remains sharp; or if the camera is panned to follow a moving subject, the background is blurred while the subject remains sharp.
The exact point at which the background or subject will start to blur depends on the rate at which the object is moving, the angle that the object is moving in relation to the camera, the distance it is from the camera and the focal length of the lens in relation to the size of the digital sensor or film.
When slower shutter speeds, in excess of about half a second, are used on running water, the photo will have a ghostly white appearance reminiscent of fog. This effect can be used in landscape photography.
Zoom burst is a technique which entails the variation of the focal length of a zoom lens during a longer exposure. In the moment that the shutter is opened, the lens is zoomed in, changing the focal length during the exposure. The center of the image remains sharp, while the details away from the center form a radial blur, which causes a strong visual effect, forcing the eye into the center of the image.
The following list provides an overview of common photographic uses for standard shutter speeds.
30-second exposure of the rotating New Technology Telescope
The Whirligig ride during night at SFGAm at an exposure time of 0.8 Seconds.
Motion picture cameras used in traditional film cinematography employ a mechanical rotating shutter. The shutter rotation is synchronized with film being pulled through the gate, hence shutter speed is a function of the frame rate and shutter angle.
Where E = shutter speed (reciprocal of exposure time in seconds), F = frames per second, and S = shutter angle:
With a traditional shutter angle of 180°, film is exposed for 1/48 second at 24 frame/s. To avoid effect of light interference when shooting under artificial lights or when shooting television screens and computer monitors, 1/50 s (172.8°) or 1/60 s (144°) shutter is often used.
Electronic video cameras do not have mechanical shutters and allow setting shutter speed directly in time units. Professional video cameras often allow selecting shutter speed in terms of shutter angle instead of time units, especially those that are capable of overcranking or undercranking.
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