Basics
Whatever camera you use, the operation is the same. A photograph is taken as
a result of light being reflected from the subject, through the camera's lens
onto the photographic plate or sensor.
If too much light is allowed in, the picture will be over exposed, and
will look bright and indistinct. If not enough light is allowed in, the picture
will be under exposed and will look dark and indistinct. It is less
common for photographs to be over exposed, than under exposed.
Aperture
Light is let in to the camera to the photograph plate, film or sensor through
a quickly opening and closing door called the shutter. The size of the hole
which is revealed by the shutter is known as the aperture, and is measured in
F-Stops, such as F1.8, F4.5, F11 etc. Where, confusingly, the larger the F
number the smaller the aperture is. Thus, F1.8 is quite a large aperture, and
F11 is fairly small. A larger aperture, represented by a smaller F number,
lets in more light than a smaller aperture. Frequently it will be found
that a smaller aperture (larger aperture number) and a correspondingly slower
shutter speed combination will result in a more accurate representation of
colours.
Shutter Speed
The length of time for which the shutter remains open, letting light in through
the aperture is often referred to as the shutter speed, and is measured in
fractions of a second. Thus, a shutter speed of 500 implies that the aperture
will be open for 1/500th of a second, while a shutter speed of 125 implies
that the aperture will be open for 1/125th of a second. The longer the aperture
remains open, the more light will enter.
Sensitivity
How quickly the photographic plate, film or sensor reacts to the light reaching
it through the aperture is known as the sensitivity of the plate, film or sensor
and is measured in ISO or ASA units. The larger the ISO value, the quicker the
plate, film or sensor will react to the light. Thus, a sensitivity of ISO 100
will react slower than a sensitivity of 200 or 400.
The aperture size, shutter speed and sensitivity, work together to determine
the level of exposure that occurs when a picture is taken. Automatic camera
settings will set these three values for you, so that the picture is properly
exposed, and if it can not be properly exposed, will warn you. However, there
are other effects connected with each of these three settings.
The higher the sensitivity of the photographic plate, film or sensor, the
more grainy or noisy the photograph will be. Therefore, using the
lowest possible sensitivity will give the best possible quality for the
photograph. In order to use a low sensitivity, the subject must be as
brightly lit as possible. For example a subject in bright sunshine or
lit by powerful lamps or the use of a camera flash gun.
Depth of Focus
The aperture size governs the depth of the photograph. The smaller the
aperture is, the deeper the field of focus. Using a large aperture size
will result in only the subject being in focus, objects behind and in
front of the subject will be blurred. Using a small aperture will allow
objects behind and in front of the subject to also be in focus. The
smaller the aperture size, the further behind and in front of the subject
objects will remain in focus, and by extension the easier it will be to
focus upon the subject.
In The following examples, four identical images were taken using aperture
sizes of F4, F8, F11 and F22. The two cigarette packets are spaced one meter
behind each other, and the camera focused on the nearer packet. You can see
that with a large aperture of F4, the packet at the rear of the picture is
significantly blurred, and this blurring reduces as the aperture size decreases
down to F22.
Camera Shake
The most noticeable effect of the shutter speed is in reducing motion blur
and camera shake. When holding a camera, particularly one with a long lens
every one will quiver their hand to a greater or lesser degree. When using
a zoom lens, this quivering or camera shake is much more noticeable
than when using a shorter or wider angle lens. If the camera is moved, even
slightly while the shutter is open, the picture will be blurred. The more
the camera moves while the shutter is open, the more blurring will occur.
By using a fast shutter speed, the shutter is open for less time and as
such less movement affect the photograph. Similarly, if the subject being
photographed moves while the image is being taken, the resulting photograph
will be blurred. Using a fast shutter speed of 1/500th of a second or faster
enables photographs to be taken of action shots, such as footballers in
mid-movement or in the air while heading the ball. The subject's movement
being slower than the speed of the shutter opening and closing which appears
to freeze the moment in time.
The best way to reduce camera shake is to use a tripod. If you can not use a
tripod, try resting the camera on a firm surface, such as a wall, fence post
or tree. It can not be over emphasised that using a tripod will result in
better photographs as every one quivers ever so slightly when taking
photographs. Even activating the shutter release on the camera can slightly
jar the camera. To overcome this, many photographers use a camera with
automatic frame advance or sequential shooting, whereby after activating the
shutter release the camera takes multiple photographs until the shutter release
mechanism is released. In this way, three images may be taken automatically,
the first and last will often suffer from slight camera shake due to the
action of operating the shutter release mechanism, while the second image
will not.
