CCTV Cameras by jasonfinney88


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									                                     CCTV Cameras

This article has been written by Jimmy Johnson. For more information visit

CCTV cameras are becoming an extremely common item in this day and age,
they offer protection and additional well being. Choosing the right CCTV
Camera lens can sometimes be tough. The information below will grant
additional information.
Closed-circuit television (CCTV) is the use of video cameras to transmit a
signal to a specific place, on a limited set of monitors.
It differs from broadcast television in that the signal is not openly transmitted,
even if it may use point to point wireless links. CCTV is often used for
surveillance in areas that may need monitoring such as banks, casinos, airports,
services installations, and convenience stores.
The use of CCTV in the United States is less common, even if increasing, and
generally meets stronger opposition. In 1998 3,000 CCTV systems were found
in New York City. Here are 2,200 CCTV systems in Chicago.
Crucial Length
The crucial length of the lens is measured in mm and directly relates to the
angle of view that will be achieved. Small crucial lengths grant wide angles of
view and long crucial lengths become telephoto, with narrow angles of view. A
“normal” angle of view is similar to what we see with our own eye, and has a
relative crucial length copy to the pick up device.

Camera Format
The size of the camera’s imaging device (CCD) also affects the angle of view,
with the smaller devices making narrower angles of view when used on the
same lens. The format of the lens, but, is beside the point to the angle of view, it
merely wants to project an image which will cover the device, i.e.: the same
format of the camera or larger. This also means that 1/3″ cameras can utilize the
entire range of lenses from 1/3″ to 1″, with a 1/3″ 8mm lens charitable the same
angle as a 2/3″ 8mm lens. The latter combination also provides increased
resolution and picture quality as only the centre of the lens is being utilized,
where the optics can be ground more accurately.
Exposure Control
The exposure in a normal photographic camera can be controlled by a

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combination of close speed and iris opening. This is not so with a CCTV
camera lens. A ordinary CCTV camera produces a complete picture every 1/2 of
the mains frequency. This is every 1/25 second where the mains frequency is 50
Hz (cycles per second) and every 1/30 second where the mains frequency is 60
Hz. Generally the exposure time is fixed and the only control of the amount of
light passing to the imaging device is by adjusting the size of the iris. This is
covered in more detail later in this chapter. Most camera tubes and imaging
devices have some tolerance of the amount of light passed by the lens to make
an acceptable picture. The range of tolerance is generally inversely proportional
to the sensitivity of the camera. The more sensitive cameras require greater
control of the iris gap.

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