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The shutter controls not only
exposure, but also the ability to stop
motion. Fast shutter speeds are
used in sport photography to stop
action. Slow shutter speeds can be
used to show the flow of motion such
as water cascading over a waterfall.
The use of a tripod is recommended
with slow shutter speeds.
The term “stop” comes from the name of aperture plates in old
lenses. Ev stands for exposure value. A change of one stop or one
Ev adjusts the exposure by a factor of two.
WHAT IS A STOP? WHAT IS AN EV?
+2.0 Ev
4X as much light
+1.0 Ev
–1.0 Ev
–2.0 Ev
2X as much light
1/2 as much light
1/4 as much light
Calculated exposure
–3.0 Ev 1/8 as much light
+3.0 Ev 8X as much light
+2 stops
+1 stop
–1 stop
–2 stops
–3 stops
+3 stops
