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- All video lines not occurring in the horizontal and vertical blacking
intervals
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- Abbreviation for automatic frequency control, a circuit built into
some VCRs
and TVs to automatically lock onto an incoming channel.
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- Audio frequency modulation is the type of audio recording used on
Beta HiFi
and VHS HiFi VCRs. The audio is laid on the tape by audio heads
located on
the video head assembly.
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- Abbreviation for automatic gain control. On a TV or VCR, AGC is a
circuit
that automatically adjusts the incoming signal to the proper levels
for display
or recording. On a video camera, AGC is a circuit that automatically
adjusts
the sensitivity of the pickup tube to render the most pleasing image.
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- After pressing 'record'', a normal VCR takes about 20 seconds before
it starts
recording usable pictures. With and alarm activated recorder it can
be set so
that the tape is ready to start recording in about one second. The
signal to begin
recording can be from an alarm or any other input
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- Photometric control, measures light intensity. Sets the iris to
react
to bright objects in a picture that does not affect the overall
video
level. Turning the control towards Peak will increase sensitivity,
towards Average will decrease sensitivity.
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- The angular range that can be focused within the image size. Small
focal lengths give a wide angle of view, and large focal lengths
give
a narrow angle of view. Sometimes referred to as Field of View.
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- The light gathering area of a lens, controlled by the iris. Relates
to the F-number. The effective aperture of a lens is not its actual
diameter but the diameter of the image of the iris seen from the
front of the lens. Larger apertures equal smaller F-number.
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- The ratio of the vertical to the horizontal image size. This is
usually 3:4.
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- This refers to signal loss in a transmission system
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- Signal-To-Noise Ratio is the ratio of pure audio signal versus noise.
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- A lens with an electrically controlled iris. The circuit controlling
the iris is set to maintain a constant video level in varying
lighting conditions.
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Automatic gain control (AGC)
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- When the light falling onto an imaging device reduces to a certain
level, there is insufficient light to create a full level video
signal. AGC acts to increase the amount of amplification in these
conditions to bring the signal up to the required level. As well as
amplifying the video signal, additional noise can be introduced, and
the signal to noise ratio reduced. The result is frequently a very
much degraded signal and poor picture on the monitor.
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- A lens that adjusts automatically to allow the right amount of light
to fall on the
imaging device. There is a tiny motor and amplifier built in which
receives a
control signal from the camera to maintain a constant one volt peak
to peak
(1.0 Vp-p) video level.
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