Digital Photography - Learn the Shutter
Speed
A camera shutter is a mechanical device
which permits light to enter the camera body for a specified
period of time. The longer the shutter is open the more light
enters the camera.
Many digital cameras have an automatic setting to determine
the appropriate shutter speed or it may be set manually for
greater artistic control.
Shutter speed is always calculated in relation to 'aperture'
– the size of the opening of the lens. These two settings are
used in conjunction to control the amount of light that hits
the image sensor.
Fast shutter speeds are used to 'freeze' action. Longer
shutter speeds can be used in low light conditions and to allow
moving objects to blur. This effect is often used when
photographing running water.
Since a fast shutter speed lets in less light than a long
shutter speed, it is usually combined with a larger aperture
setting to allow sufficient light to reach the image sensor.
likewise, long shutter speeds are combined with small
apertures.
Shutter speeds are measured in fractions of a second in an
approximate 2:1 scale starting with 1 second. The scale runs 1
second, 1/2 second, 1/4 second etc. down to the fastest speed
of 1/8000 second. In addition, many cameras have a 'B' shutter
setting (the shutter stays open as long as the button is
pushed) and a 'T' setting (the shutter stays open until the
button is pushed again).
Aperture settings are also measured on the same 2:1 scale.
This allows for the same light exposure by increasing shutter
speed one notch while opening the aperture one notch. Light
conditions for a given scene allow for a range of shutter
speed/aperture combinations. There is no 'correct' combination
– it depends on what kind of effect the photographer hopes to
capture.
For instance, if you want to capture a moving
subject such as an athlete during a sports competition, you
would normally use a fast shutter speed to freeze the action.
This fast speed must be used with the correct aperture to
expose the image correctly.
A slower shutter speed, however, could be used if you pan
the camera to match the movement of the athlete. This can
create a more dynamic effect as parts of the picture
(especially the background) will be blurred. Slower shutter
speeds must be compensated for with smaller aperture
settings.
Another common photographic effect is controlling the depth
of field to highlight the subject. Large apertures have a
smaller depth of field which means that the foreground and
background will be (pleasingly) out of focus. To achieve this
effect you must combine the large aperture setting with a fast
shutter speed.
Flash adds another dimension to the aperture/shutter speed
equation. Interesting effects can be achieved by using flash to
freeze the main motion while allowing some of the action to be
blurred with a slower shutter speed.
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