Learning Event 3
CALCULATE SHUTTER DURATION
1. The shutter controls the length of time light is allowed to react on the
light sensitive material. This time is divided into fractions of a second,
known as shutter speeds.
Shutter speeds are usually written as fractions
such as 1/125, 1/250 and so on.
The appearance of the action in a
photograph can be controlled by using different shutter speeds.
A fast
shutter speed will freeze, or stop the action.
Where as a slow shutter
speed will help create the illusion of motion.
Shutter speeds will vary
based on the amount of available light, and the speed of a moving subject.
The most common shutter speeds available for modern cameras are: T (time), B
(bulb), 1 second and fractions of a second of: 1/2, 1/4, 1/8, 1/15, 1/30,
1/60, 1/125, 1/250, 1/500, 1/1000 and 1/2000.
a. By using the setting marked "T" (time), the shutter will open when
pressure is applied to the shutter release button and will remain open until
pressure is again applied to the shutter release button.
This setting is
normally used for exposure times that require minutes or even hours and
allows you to leave the camera in place during exposure until you return at
a time you selected to reapply pressure to the shutter release button.
b. On the setting marked "B" (bulb), the shutter will open when
pressure is applied to the shutter release button and will remain open until
the pressure is released. This setting is normally used for exposure times
requiring two or more seconds. Once pressure is released from the shutter
release button the shutter will close.
Use of a tripod is required for
exposures of "T" and "B" as the camera must remain motionless during
exposure.
c. The remaining shutter speed selections re a full one second and
fractions of a second. Changing shutter speed to the next indicated speed
will either double the duration of shutter opening or decrease the duration
of shutter opening by one half.
For example, if a shutter speed of 1/60
allows one unit of light to pass through, then the next slower shutter speed
of 1/30 will allow two units of light to pass through. A shutter speed of
1/125 will allow one half as much light or one half of a unit of light to
pass through than 1/60.
2. Shutter speeds are referred to as faster or slower shutter speeds as
related to each other. Thus, 1/250 is a faster shutter speed than 1/125 and
below, but slower than, 1/500 and above. It is proper to say that 1/250 is
two times faster and allows one half the amount of light as 1/125 and 1/60
is one half slower and allows two times the amount of light as 1/125.
Therefore, if a 1/500 allows one unit of light, 1/250 will allow two units
of light (two times more), 1/125 will allow four units of light (four times
more), and 1/60 will allow eight units of light (eight times more) as 1/500.
Notice that each change in shutter speed allows two times (2X) more or 1/2
less light (see table 3-1).
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