Shutter speed

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The Shutter Speed is one component factor of exposure. It refers to the amount of time the shutter is open, usually expressed as a fraction of a second (or a number of whole seconds).

Manually-set shutter speeds (at least in fairly modern cameras) usually accord with a standard series: 1, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500 and 1/1000 second are common; more speeds are offered at both ends of this series by some cameras. Many older 20th-century cameras have 1/5, 1/10, 1/25, 1/50 and 1/100 second instead of 1/4 - 1/125.

Surprisingly, focal-plane shutters offered speeds of 1/1000 second (or even faster: see the Deckrullo-Nettel for example) at least as early as the 1920s; leaf shutters faster than 1/500 second are rare, however.

A simple shutter may offer only a single instantaneous speed, 'I'; this is typically 1/30 - 1/50 second. Most adjustable shutters also offer 'B' mode (Variously taken to stand for 'Bulb', after the pneumatic hand-bulb used to release early shutters, or 'Brief-time'; sometimes denoted 'P' for 'Pose' in French cameras, and 'M' for 'Moment' in some German ones); in 'B' shutter mode, the shutter opens when the button or lever is pressed and remains open until it is released. Some shutters also offer 'T' mode (denoted 'Z', for 'Zeit' in some German cameras), where the shutter opens when the button is pressed, and remains open until it is pressed a second time.

Slow shutter speeds can give visible blur in the picture due to movement of the subject (this may or may not be desired), or due to camera shake during the exposure (this is rarely desired). A high speed can freeze fast action and avoid camera-shake.

Slow shutter speeds may allow small lens aperture, giving greater depth of field, whereas high speeds can be used with large apertures - using deliberately shallow depth of field to separate a subject from an out-of-focus background.

Fast shutter speed may be possible in low-light situation with high-ISO film (or high-ISO setting of a digital camera), but may give results with less image resolution or more noise.

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