This prevents unwanted vibrations which occur when you hold the camera.
Some cable releases have a locking device which will let you make a long
exposure without having to stand there with your thumb on the plunger the
c. Mechanical shutters, whether leaf or focal plane type, can't be set
to an intermediate speed for the same reason you can't select a gear between
second and third while driving a car.
For example, there is no way to
select a 1/245 second or a 1/320 second shutter speed. This isn't really
much of a problem, because lenses can be set to intermediate f/ values. The
big advantage of purely mechanical shutters is that they don't rely on
A cable release
d. Electronically-controlled shutters, which are made for both leaf and
focal plane types, need a source of electricity. These shutters still rely
on springs to make the larger parts move, but their timing is controlled
electronically. This makes the mechanism smaller and lighter, because a lot
of complicated timing gears are eliminated in favor of a very small computer
The shutter speed range is often extended to include full second
exposure times of 2, 4, 8, and even longer.
(1) Electronic shutters can also operate at intermediate speeds, but
usually only when the camera is operating in an "automatic" mode. They also
have fewer moving parts, which make them less likely to break.
negative side, though, these shutters use batteries, which can fail at
unexpected times (usually the worst possible moment), and almost always in
(2) If your camera uses an electrically-controlled shutter, always
carry a spare battery with you; and if you are planning to shoot in below-
freezing conditions, try to find a camera with a completely mechanical
Some camera makers do provide an accessory battery pack with a
long wire attached. This allows you to keep the batteries in a warm inside
pocket and still provide power to the camera. It's a bit cumbersome, but it
Learning Event 4:
DESCRIBE HOW TO DETERMINE EQUIVALENT EXPOSURES
Now to put some of this together.
Remember what was said about
equivalent exposure a few pages ago - how there could be any number of
combinations of light intensity and time which would result in the same
Well, now you have an easy way to compute as many equivalent
exposures as you wish, and then to select the one which suits your purpose
best. Let's put the two scales together as in Table 1-6.