Selecting the correct components for a CCTV system is always seen as being easy, however there are some basic rules of thumb which if used correctly will result in a correct specification and selection of components first time without resorting to costly changes post installation.
Choosing the right camera is the first part, the images available to the operator/recorder start with getting this choice correct, your choice will depend upon the answers to a few basic questions.
Colour or Black & White?
Colour camera's are for daylight or artificially white light illuminated area operation only, they provide powerful information aiding surveillance teams with description such as ethnicity of suspect, colour of clothes worn by a suspect etc.
Black & White camera's are used in poor lighting and night time operation, they can be aided with infra red (invisible) lighting and are ideal for most applications.
Day/Night Colour camera's are designed to provide the best of both, returning a colour image in daylight or white light illumination but automatically switching to black & white after dark, once again, infrared (invisible) light can be used to aid the performance in total darkness.
Choosing the correct lens for the camera is an area many specifiers find difficult, lens selection calculator tools are available and even devices which look like a telescope allowing a specifier to stand where the camera will be located and select a suitable lens however both these devices suffer problems, it is not always possible to stand where a camera will be located, it is not always possible to have the client agree upon the selection at the time of specification as a result.
Care should be taken that the lens purchased will fit the camera mounting and is designed to work with the size of CCD chip within your camera, in addition auto iris or electronic iris variants are needed to suit the camera.
In general use there are 5 main lens types
Wide angle = A lens providing approximately 56° horizontal field of view
Standard = A lens providing approximately 30° horizontal field of view
Telephoto = A lens providing approximately 16° horizontal field of view
Varifocal = A lens providing the commissioning engineer to set the field of view anywhere between 56° and 16° horizontal field of view (some may vary slightly)
Zoom = A lens providing an adjustable field of view controlled by your customer usually given a a ratio of the angles at wide and telephoto ends i.e. 10:1 = 56° to 5.6° - 18:1 = 56° to 3.1°
CCTV experts will know instinctively what lens should be specified, for your first few installations, supplying varifocal lenses for all fixed cameras will give the maximum flexibility during commissioning.
Zoom lenses are only used on cameras capable of being remotely controlled by your customer i.e. pan, tilt and zoom (PTZ)
To obtain the correct lens for your camera you will need to know the following:
The size of the CDD chip 2/3" 1/2" 1/3" or 1/4" ( an 8mm lens will provide a wide angle view on a 2/3" chip and a telephoto view on a 1/3" chip.
The iris control type, choice of
CWV (centre weighted video for cameras supplying a video image to the lens allowing the lens to adjust brightness).
DD - the most common (direct drive for cameras which control the iris directly to adjust brightness).
Manual Iris (for cameras using variable fast shutter speeds to adjust picture brightness)
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