camera in manual mode, you must understand the
relationship between the f/stop and shutter speed.
Shutter speeds are indicated so that each marked
shutter speed admits one-half or two times the adjacent
marked speed. Since both the lens aperture and shutter
speed represent full stop changes in exposure, either
can be moved as long as the other is moved a similar
number of stops to compensate. A basic exposure of
1/125" at f/16 can be changed to 1/500" (two stops less
light transmitted) at f/8 (two stops more light
transmitted), and the result will be the same total amount
of light transmitted to the film.
Shutter speeds cannot be set between marked
stops. If an exposure is calculated to be 1/40" at f/8,
using the closest shutter speed available on your camera,
1/30" or 1/60" will not result in an exposure error
because of the exposure latitude of the film. An
alternative is to set the shutter speed and an equivalent
half-stop of lens apeture, such as 1/30" at f/9.5, or
1/60" at f/6.3.
With a selection of possible combinations, which
should be used? Does it matter which is used? Why does
the manufacturer put so many combinations on the
Before these questions are answered, you must
understand the correlation of lens apertures and shutter
speeds. Think of the lens aperture as a water pipe (the
larger the diameter of the pipe, the more the water can
flow). Extending this further, think of the film sensitivity
in terms of a bucket that has to be filled and the light
intensity as the water pressure.
If a bucket can be filled in 1/30" with a pipe 8 square
inches in area, how long would it take to fill using a pipe
4 square inches in area? Obviously, twice as long
1/15". If the exposure is calculated at 1/30" at f/11, how
long an exposure is required at f/16 (the aperture
one-half the area of f/11)? The answer is 1/15".
What happens if the water pressure increases? It
takes less time to fill the bucket. If we use a larger bucket
(lower ISO film speed), it takes more water (exposure)
to fill it.
Shutter Speed Considerations
Generally, the shutter speed is chosen according to
the amount the subject moves or how much of the
movement you desire to show. If the subject moves
slowly, a slower shutter speed can be used; if the subject
moves rapidly, a faster shutter speed must be used to
stop the movement and prevent blurring the image.
Movement of the camera and photographer also must be
considered. Therefore, the use of a tripod or similar
brace is advisable when using a shutter speed slower
than the reciprocal of the lens focal length; for example,
50mm lens (1/60"), and 200mm lens (1/250").
To stop the movement or action in a picture, you
must consider the following three factors:
l The relative movement of the subject
. The subjects direction of movement
. The camera-to-subject distance
THE RELATIVE MOVEMENT OF THE
SUBJECT. The faster the movement, the faster the
shutter speed required. The term relative movement is
used because if the motion of the subject is followed,
that is, the action is panned with the camera, a slower
shutter speed can be used than if the camera were held
THE SUBJECTS DIRECTION OF MOVE-
MENT. A subject traveling at a right angle to the
camera/lens axis requires a faster shutter speed than one
traveling at a diagonal. Conversely, a subject moving
toward or away from the camera, parallel to the lens
axis, can be stopped with a slower shutter speed than
movement in other directions (fig. 11-21).
THE CAMERA-TO-SUBJECT DISTANCE.
The closer the action is to the camera, the faster the
shutter speed must be. A car traveling 60 miles per hour
across the lens axis at a distance of 100 feet would be
stopped by a shutter speed of 1/1000" (or perhaps
1/500"). However, if the camera-to-subject distance
were increased to 500 feet, the action could be stopped
with a shutter speed of 1/250" or 1/125." If the car was
a half mile away, 1/60" should be sufficient to stop the
DEPTH OF FIELD
Selection of a f/stop is done mainly for the desired
depth of field. Depth of field is defined as the distance
between the nearest and farthest points of acceptable
sharp focus of the scene photographed (fig. 11-22).
Control of the depth of field is a valuable tool in
photography. Depth-of-field charts are given in all
camera instruction books as well as in photographic
reference manuals, but many photographers fail to use
them to their own advantage.
Simply stated, depth of field increases as the focal
length of the lens decreases (a shorter focal-length lens
is used), as the lens aperture decreases (gets smaller in
size) and as the distance focused on (focal point)
increases, or both. Inversely, depth of field is less for
long-focal-length lenses than for short-focal-length