CHAPTER 13
MOTION MEDIA
Motion media has gone through many technical
advances in the past several years. Portable motion-
video cameras have changed from cumbersome
cameras and recording packs to small hand-held
cameras. Reduced size, improved quality, and easier
operation has, and is continuing to improve and
expand motion video in all areas of the Department of
Defense. Most Navy ships have closed circuit
television systems for information, entertainment,
and educational purposes. Motion media is distributed
easily and dominates all other sources of
communication in today's society. Because of this, the
Navy uses this form of communication extensively to
relay information.
The most common form of motion-media photog-
raphy is video. Since the motion picture is the grand-
father to the technology of motion media as we know
it today, it is discussed briefly in this chapter.
MOTION PICTURE
The first fact regarding motion pictures is they do
not move. Each image or frame of motion picture film
is a separate, still photograph. These individual
images or frames are normally recorded at a rate of 24
separate pictures per second. This rate can be varied
to achieve certain effects. Since so little time passes
between exposing one frame and the next, there is
relatively little difference between pictures, even
when the subject moves rapidly.
The illusion of motion in motion-picture photog-
raphy is due to the natural characteristic of human
vision. This characteristic of human vision is called
persistence of vision. Persistence of vision was
discovered by Peter Mark Roget, the author of the
famous Thesaurus. The retina of the eye continues to
perceive an image for a short period of time after the
light stimulus representing the image has been
removed. Usually, this "after image" lasts about 1/50
second, depending on the brightness of the image.
In viewing a motion picture, the eye continues to
perceive the fading image projected from one frame
as it is replaced by the next frame, and so on. In effect,
the images are momentarily superimposed in our
vision, so any differences between them, however
slight, are mentally noted. If these differences
suggest any relative change in subject position, the
apparent difference is mentally interpreted as
motion. The mind translates this information into
the logical deduction that whatever we are seeing
on the movie screen must be moving.
CAMERAS
Since motion pictures are a series of still pictures,
the motion-picture camera is basically the same as the
still-picture camera. The primary difference is that it
has a mechanism for taking a series of many
photographs in rapid succession and at regular
intervals on a ribbon of film. All cameras have the
following four basic parts: a lighttight compartment,
a lens or lenses, a shutter, and a film plane or pressure
plate.
The motion-picture camera has two additional
basic features; the film drive and intermittent action.
The film drive mechanism transports the film
continually from a supply spool of unexposed film to
a take-up spool of exposed film. This transport takes
place by means of toothed, drive sprockets. The teeth
of the drive sprockets engage the perforations along
the edge of the film and move the film through the
camera.
The intermittent action in a motion-picture
camera is caused by a pulldown claw that advanced
the film one frame at a time at the film gate.
During one cycle of operation of a motion-picture
camera, the following action takes place. The film is
advanced by the sprocket drive mechanism. The
pulldown claw or shuttle then advances the film one
frame. The film is stopped momentarily and the
shutter revolves once, thereby making the exposure.
The pulldown claw then moves the film to the next
frame for exposure. Because the film moves in an
intermittent or stop-and-go manner, it becomes
necessary to have a surplus or loops of film before
and after the pulldown claw to help take up the
13-1

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