Camera
operation described
here is essentially
what happens inside
the camera to
make it work.
At the film gate
immediately behind
the lens, a claw
reaches up and
hooks into a perf
on the film and
pulls it down,
centering a single,
unexposed frame
of film at the
gate. The shutter
opens and exposes
the film (takes
a photo). As the
shutter closes,
the claw reaches
up and draws down
the next unexposed
frame as more
film is transported
from the magazine's
supply reel into
the camera body
and fed toward
the film gate.
The exposed frames
exiting the film
gate are drawn
down by a toothed
sprocket in the
body and transported
toward the take-up
reel in the magazine.
The take-up reel
neatly winds the
exposed film so
it can be neatly
removed and shipped
to the lab once
the supply reel
has emptied. That's
more or less what
goes on inside
the camera when
it's running,
usually at twenty-four
times a second.
FIXED
& VARIABLE
SHUTTERS
A
shutter is a light
blocking device
which controls
the duration of
light exposure
to the film negative.
The primary function
the shutter performs
is to establish
a consistent exposure
- the film has
to be stationary
to receive an
unblurred image
(move the film
during an exposure
and you've got
a blurred image),
so the shutter
is timed to unblock
the negative in
the film gate
only when the
film has momentarily
paused and receives
the light of the
image transmitted
through the lens;
following the
exposure, the
shutter blocks
the film gate
and the film is
advanced behind
the shutter to
the next unexposed
section of film.
Once an image
is burned in the
film gate, it
becomes a frame.
The second function
performed by the
shutter is found
only in a Variable
type shutter.
Just like the
shutter speed
of your 35SLR
still camera,
a variable shutter
provides the means
to reduce the
duration of exposure,
independent of
the frame rate
(frames or exposures
per second). Since
motion picture
film in the USA
exposes at a rate
of 24 frames per
second, a motion
picture camera's
theoretical shutter
speed is 1/48
of a second -
at best. In fact,
most shutters
run slightly faster.
If you've shot
stills at a shutter
speed under 1/100th
of a second, you
know that shooting
a moving object
will blur. You
also know that
to kill that motion
blur, you'll have
to speed the exposure
up (which also
means you'll have
to go to a wider
F/stop to maintain
the same overall
exposure). In
a motion picture
camera, the exposure
can be sped up,
not by spinning
the shutter faster,
but by reducing
the angle of the
shutter. That's
why shutter speed
on a motion picture
camera is graduated
in degrees.
