(4) Video noise.
Under low light levels, even the best of cameras
cannot avoid "noisy" pictures.
A "noisy" picture has a great amount of
snow, or white vibrating spots in the picture. This occurs when the video
signal as produced by the pickup tube is not strong enough to override the
electronic interference that the system usually generates.
(a) Video noise works very much like audio noise. Even the best
high fidelity system has some inherent electronic noise. You can hear the
speakers hiss a little as soon as you turn on the amplifier. Or, when the
music is very low, which is equivalent to a weak audio signal, you may
become aware of the rumble of the turntable.
As soon as the music gets
louder again, equivalent to a stronger audio signal, you are no longer aware
of the noise.
(b) The relation of the strength of the picture signal to the
accompanying interference, the noise, is generally expressed in a signal-to-
noise ratio. A high signal-to-noise ratio is desirable. It means that the
signal is high (strong), relative to the noise under normal operating
conditions.
(5) Lag or comet tailing.
Lag is the following image that occurs
under low lighting conditions, especially when a bright object moves against
a dark background, or when the camera moves past some bright objects against
a dark background.
(a) Lag occurs quite frequently during the televising of a
concert.
For example, when watching a concert on TV, you may notice that
the conductor's white cuffs and baton causes large color streaks against the
dark background of the dark house. The same effect occurs when televising a
football game as the players run from a brightly lighted area of the field
to a shadow area and they suddenly seem to emit streaks of red flames.
(b) Comet tailing is similar to lag, except that it occurs when
the camera pickup tube is unable to process "video hits," extremely bright
highlights that are reflected off highly polished surfaces.
You may have
observed red flames that seem to tail shiny trumpets whenever they are moved
in a brightly illuminated area. This effect is called comet-tailing because
the red flames resemble the fiery tail of a comet.
10. Viewfinder. The viewfinder is relatively small, about 1.5 inches, but
produces a high image.
It is shielded from outside reflections by a
flexible rubber eyepiece that you can adjust to your eye.
a. The viewfinder contains a number of control lights or displays that
indicate the status of certain camera or production functions.
Most
viewfinders display, automatically, some or all of information on VR
recording, tape warning, and battery status.
b. Most viewfinders display, on command, color bars, patterns, white
balance, black balance, and registration of camera.
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