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The Camera
Cameras convert the visible scene captured by a lens into
an electric signal and transmit that signal to a
monitor for viewing.
Several considerations should be taken into account when choosing the proper
camera/lens for any video system:
| • |
The purpose of the video system (detection,
assessment, identification, ect.) |
| • |
The overall sensitivity of the camera needed based
upon the actual application |
| • |
The amount and varying levels of light available
at the scene |
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The environment in which the camera will operate
(indoors/outdoors) |
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The field of view (FOV) required by the
application (see figure 3) |
| • |
The lens |
| • |
Cost |
Figure 3: Field of view.
Camera performance depends largely upon the reflected
light at the scene and the quality of the
cameras imager (see figure 4).
Where the level of available light can change dramatically, a camera equipped
with automatic iris
control can help assure consistent image quality. Automatic iris control enables
cameras to open or close an auto iris lens to adjust the amount of light passing
through the lens. On a bright, sunny day, for example, an auto iris camera will
close the lens' iris to prevent strong light from reaching the camera's imager.
At night, the camera will open the iris to allow a greater amount of light into
the camera.
Cameras are available in various "formats" expressed as1/2, 1/3, or1/4 inches.
These measurements represent the overall usable size of the camera's imager. In
general, you should match the camera's
format to the lens format. For example, a half-inch camera should be paired with
a half-inch lens.
Today, thanks to design improvments, high quality images are possible with
smaller formats.
Figure 4: The imager (or chip).
Fixed and PTZ Cameras
CCTV cameras can be fixed or have pan, tilt and zoom (PTZ)
capability. Fixed cameras are mounted on a fixed bracket and cannot move in
response to operator commands. PTZ cameras are motor driven and can pan left and
right, tilt up and down and zoom in and out for close-up or wide-angle viewing.
(See figure 5)
Figure 5: PTZ camera.
A cameras housing protects the camera and lens from
vandalism and the environment. It also can enhance the appearance of the camera
installation and conceal the equipment from casual observation. All outdoor
cameras require a housing of some type. The National Electrical Manufacturers
Association (NEMA) rates housings on their ability to withstand environmental
conditions. Protection from cold, heat, dust, dirt or other elements is needed
to ensure optimum performance and extend the life of the camera.
Dome Cameras
Many PTZ cameras today are disguised in dark colored
Plexiglas housings called domes. Dome cameras are found practically every major
department store and in many industrial/commercial locations, hospital, colleges
and government facilities (See figure 6). They are particularly popular wherever
aesthetics are valued.
Dome cameras provide three primary benefits:
| 1) Deterrence |
Domes make it virtually impossible for suspects to determine
where the camera is pointed. Individuals planning to commit criminal
activity are unable to detect whether or not they are under active
surveillance. |
| 2) Economy |
Domes equipped with a camera, lens, and pan/tilt unit can be
augmented with "drones" that have the same outward appearance, but have no
equipment inside. The result is more apparent camera coverage with a much
lower system expense. |
| 3) Aesthetic Appearance |
An exposed camera, lens, pan/tilt unit and associated wires
are
unsightly. A dome makes the collection of equipment more aesthetically
acceptable, and does not detract from the interior design of a retail or
business office environment. |
Placing a mirrored finished or smoked bubble around the
dome can conceal a dome camera further.
However, when this is done, the bubble has the effect of sunglasses, reducing
the amount of light reaching the lens and affecting the color accuracy picked up
by the camera.
Figure 6: Dome cameras.
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