speed dial, the top part of the fraction (numerator) is not
indicated; for example, the shutter speeds 1/60, 1/125,
1/250, and so forth, are indicated as 60, 125, and 250.
When a camera with a focal-plane shutter is used
with an electronic flash, a predetermined shutter speed
must be set. At this speed the shutter and flash unit are
said to be in synchronization. When the flash and shutter
are synchronized, the shutter opening is wide open at the
same instant the flash fires. Usually, the slowest shutter
speed that syncs with a flash unit is indicated in red or
another off color or a lightning bolt symbol on the
shutter speed dial.
Function
The shutter serves two functions: controlling the
duration of the exposure and controlling subject
movement. These two functions are entirely separate
and distinct. You must determine the shutter speed
required for each condition. After determining the
shutter speed, you select the f/stop that provides the
correct exposure for the film speed and lighting
conditions. Normally, the duration of exposure is short
enough to prevent image blurring. You can always set
the shutter speed faster than the speed required to stop
image motion, but it should not be longer if you want
the image to be sharp; for example, when a shutter speed
of 1/125 is sufficient to stop subject motion, you can set
the shutter speed to 1/250 or faster, but not at 1/60 if you
want to stop the motion and produce a sharp image. Each
time you change the shutter speed, the diaphragm is
adjusted to produce a properly exposed image.
The correct sequence in determining the diaphragm
and shutter to produce a properly exposed negative is as
follows:
1. Compose and focus the image.
2. Stop down or open up the diaphragm until the
desired depth of field is achieved.
3. Select the shutter speed that will produce a
proper exposure when combined with your
aperture setting.
4. Determine whether the shutter speed is fast
enough to prevent image blurring.
5. If the selected shutter speed is too slow, reset it
to a faster speed and open up the aperture
accordingly.
When you increase the shutter speed, you
compromise and loose depth of field. Sometimes this is
the only way to produce a useable image. If you cannot
sacrifice some depth of field, there are several
alternative you can use: select a faster film, increase the
camera-to-subject distance, select a shorter focal length
lens, or change the camera angle, so the relative motion
of the subject to the camera is decreased.
Selecting the Shutter Speed
Knowing what shutter speed produces the right
effect for each picture is a skill you, as a Navy
Photographer's Mate, must acquire. Your pictures may
easily be spoiled by movement of either the camera or
the subject. In some instances, this movement can
actually improve your photographs.
Novice photographers often find it hard to believe
anything can happen during the brief instant the camera
shutter is open. This is not true; images can be blurred
when a shutter speed as fast as 1/250 of a second is used;
for example, when the camera or subject moves during
the fraction of a second the shutter is open, the image
may be recorded on the film as a blur. Blurring caused
by camera movement is noticeable in all images within
the photograph. When blurring is caused by subject
movement only, the background or some other part of
the scene will be sharp, and the subject blurred. Camera
movement blur can be corrected by supporting the
camera properly or by using a faster shutter speed.
Subject image movement can be reduced by using either
a faster shutter speed or by panning the subject.
As explained previously, when a faster shutter speed
is used, a wider aperture is required to produce correct
exposure. For this reason you should know what
minimum shutter speed is required to stop or freeze
different actions. You must take into account conditions
that exist when taking photographs. Strong winds,
vibrations, or a ship rolling from side to side must be
considered. There is a general rule you must follow for
determining shutter speed when handholding a camera.
The slowest shutter speed recommended to prevent
camera movement blur is to set the shutter speed so it
matches the focal length of the lens. When a shutter
speed does not exist for the focal length of the lens,
select the next highest shutter speed; for example, 1/30
second for a 25mm lens, 1/50 second for a 50mm lens,
1/125 second for a 100mm lens, 1/250 second for a
200mm lens, and so forth.
When a subject is in motion during exposure, the
image on the film also moves. Even though the duration
of exposure may only be 1/1000 of a second, the image
moves a small fraction of an inch during this time. The
problem you encounter is how much image movement
4-14

Basic Photography Course












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