Graphics Reference
In-Depth Information
The depth of field may be determined by a number of factors, such as the lens
aperture, the distance of the subject from the camera, and the focal length of
the lens being used. The depth of field may be adjusted using a combination
of these controls to create the desired effect:
•
Lens aperture.
The wider the aperture the iris is set at, the shallower the
depth of field becomes; the narrower the aperture, the greater the depth of
field. When you're adjusting the lens aperture, you can ensure the correct
exposure if you compensate for the light levels by the duration of the expo-
sure. Increasing the lens aperture will not only let more light fall onto the
sensor, it will shorten the depth of field. As a result of the increase in light,
a faster shutter speed will be required to maintain the required exposure.
Conversely, by decreasing the aperture, less light will fall on the sensor;
therefore slower shutter speeds are required to achieve a correct exposure.
As a result of this narrower aperture, the depth of field will be lengthened.
•
Focal length of the lens.
The focal lengths of different lenses will result
in varying depths of field in specific series of shots. With the figure at a
given distance from the camera, the depth of field is increased as the focal
length of the lens is decreased. In this instance a wide-angle lens with
a shorter focal length, such as a 28mm lens, has a greater depth than a
standard 50mm lens, which will in turn have a greater depth of field than a
telephoto lens with a focal length of 300mm.
•
Distance of subject from camera.
The depth of field will also change in
relation to the distance the subject is to the camera. Using the same lens
of the same focal length with the same aperture setting, the depth of
field will increase the further the subject is from the camera. This principle
applies to lenses of all focal lengths.
f/22
FIG 7.25
A wider aperture (low
f-stop value) results in a shallower
depth of field.
f/8
f/2.8
Lighting and the use of flash photography enable another approach to action
analysis, though one that needs a higher level of control and thereby has
built-in limitations.
Chronophotography
is the recording of several images
