Digital Photography - Aperture
The shutter decides how much light
enters the camera, and there are two settings which are related
to the shutter -- aperture and shutter speed.
Aperture is the size of the opening between the lens and the
image sensor. Large apertures allow more light to enter the
camera than small apertures. Apertures are expressed in 'f'
numbers -- the higher the number the smaller the
aperture. Standard lenses are usually rated between f/1.8
and f/16.
Each f-number allows twice as much light to enter the camera
as the previous f-number. For example, f/8 produces an exposure
which is twice as bright as f/16.
Aperture settings have two basic effects -- the amount of
light which strikes the image sensor, and the 'depth of field'.
Depth of field refers to the length of the image which is in
focus. Large aperture settings have a shallow depth of field --
this means that the focus of an image is relatively short which
causes foreground and background objects to appear out of
focus. Small apertures have a deep depth of field -- almost all
the objects (foreground and background) will remain in
focus.
Aperture is directly related to shutter speed for
determining the amount of light that enters a camera. Large
apertures combined with fast shutter speeds let in the same
amount of light as small apertures combined with slow shutter
speeds. Determining which combination is best for a
particular situation requires photographic judgment that comes
with experience.
Most cameras have an automatic setting which will do the
calculations for you. Many photographers, however, wish to
control aperture and shutter speed for artistic effect.
Since a large aperture can be used in conjunction with a
fast shutter speed, this is often a good combination for action
shots because the fast shutter speed will 'freeze' the motion
with a minimum of blurring. Large apertures can also be used
for low light conditions where there is very little movement in
the scene. In this situation you would combine the large
aperture with a slow shutter speed.
Simple point-and-shoot cameras usually have a fixed
aperture, and it is only with more expensive models that you
have adjustable aperture settings. When choosing a digital
camera, one consideration should be the aperture range. There
are several ways this can be expressed in the camera
specifications: maximum aperture, aperture range, maximum
wide-angle and maximum telephoto apertures.
It is more useful to know the aperture range of a particular
camera rather than the maximum apertures. A larger range gives
you more flexibility in the kinds of shots you can take.A good
range for all purpose photography is from f/1.8 to
f/16.
Each lens has its own aperture rating. Telephoto lenses
typically have a shallower aperture range than wide-angle
lenses because longer lenses need proportionally more light.
This is because they are gathering light from a smaller source,
so larger apertures are needed to produce f-numbers which are
consistent with shorter lenses.
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