Automatic Gain Control:
Many cameras come with an AGC circuit. This circuit examines the brightness level of
the video signal to keep it at a consistent level. For example, if the video signal is dark, it will
attempt to increase the gain to bring the brightness up to a normal level.
In CCTV optics, the aperture is the diameter of the lens that controls the amount of light reaching
the image sensor. It is shown by an f-number. Larger aperture lenses have smaller f-numbers. For
instance, a lens with an f-number of 1.2 will allow more light to reach the sensor than a lens with
an f-number of 2.0 thus producing a brighter image. The higher the f number the less light is permitted
to pass into the camera.
An automatic iris lens is a lens with a motorized iris that automatically adjusts to only allow a specific
amount of light to reach the image sensor. When there is little light, the iris will open to let more light
in. When there is too much light, the iris will close to reduce the amount of light let in. Auto iris lenses
are primarily used in applications where light levels vary and it would be impracticable to manually adjust
the lens. Automatic iris lenses are generally more efficient than the electronic shutter since they actually
control the amount of light reaching the sensor as opposed to simply adjusting shutter speed.
Back Light Compensation:
Many cameras include a BLC circuit. This circuit is used to help correct an image with more light
behind the subject being viewed. Without backlight compensation, the subject appears dark with little detail.
Using the backlight compensation will reduce the brightness of the light to allow the subject to appear brighter
and bring out the details.
Common formats are 1/4”, 1/2”, 1/3”, 2/3”, and 1”. The size of the sensor
directly affects the field of view obtained. When using the same size lens on different format sensors,
different viewing areas are obtained. For example, using a 6mm lens on a 1/3” sensor will give you
a 37º field of view. Using the same lens on a 1/2” sensor will increase the field of view
to 56º and 74º on a 2/3” sensor.
C Mount Lenses:
An industry standard for lens mounting. The C-Mount has a thread with a 1 inch diameter and 32 threads
per inch. The distance from the lens mounting surface to the sensor surface is 0.69 inches (17.526 mm).
It is possible to mount a C mount lens onto a CS mount camera with the use of a CS adapter ring.
CS Mount Lenses:
An industry standard for lens mounting. The CS-Mount has a thread with a 1 inch diameter and 32 threads
per inch. The distance from the lens mounting surface to the sensor surface is 0.492 inches (12.5 mm).
It is not possible to use a CS mount lens on a C mount camera.
EXview HAD CCD is a trademark of Sony Corporation. The HAD CCD dramatically improves light efficiency by
including near infrared light as a basic structure of the sensor. Conventional CCD sensors are sensitive to
infrared light but are unable to efficiently gather the charge. Because of this greater efficiency, HAD CCD
sensors achieve sensitivities approximately 4 times that of a conventional CCD.
The area below the visible spectrum. B&W cameras are very sensitive to infrared light and allow the use
of infrared illuminators to enhance poorly lit locations without alerting subjects during surveillance. Color
cameras are also sensitive to infrared light, but require an infrared filter to filter out the red light to
keep the image colors.
The Super HAD CCD is a version of Sony’s high performance HAD with improved sensitivity from the use
of more efficient on-chip microlenses. The Super HAD optimizes the shape of the on-chip lenses in order to
minimize the ineffective area between the lenses on each pixel thereby minimizing lost light and improving
the overall sensitivity per pixel.
Color cameras only. Different lighting sources provide different color temperatures. The white balance
helps correct these differences by adjusting the color processing to bring the color temperature to a
fixed level. Without this balancing feature, due to the CCD’s poor adaptability, some colors would
appear different (green instead of white in sunlight).