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With PTZ units, automatic operations can give a casual observer the impression that the cameras are in constant use (increasing the deterrent effect); but of course with Dome cameras, there are no outward signs of any movement, so there is effectively no enhanced deterent effect.
Well, consider a surveillance camera mounted on a pole at a cross roads (intersection) in the middle of a town; the camera can be manually or automatically made to look in one of four possible directions at any one time (so in practice 25% of target locations in view, 75% of total area of possible coverage not being watched).
Given that the lens settings provide a variation from wide angle, perhaps 0.4x magnification, through to 20x telephoto (many modern optics are significantly more powerful than this), the likelyhood of a lens being set at the optimum zoom and focus settings for passive observation could again be suggested somewhat optimistically at around 25% probability; this then reduces the apparent effectiveness of our example camera to just over 6% efficiency at any given time.
If you also consider that the Town Centre may enjoy coverage from possibly thirty different cameras (its only an average system), and the operator can only really concentrate on effectively monitoring perhaps eight at a time, the final efficiency estimate begins to look somewhat embarassing. It's worth remembering that most Local Authority CCTV control rooms accept feeds from scores if not hundreds of cameras.
With a camera being left on a static set up (i.e. not under any manual or automatic control of movement or lens settings), there is approximately a 6% chance of an incident or suspect being recorded although not necessarily to a reasonable standard of evidential quality.
If you take into account the total number of cameras in a typical Town Centre system, the odds of a Control Room Operator actually spotting a suspect or incident, are further reduced to just over 1.5%, for a single camera that may well have cost around £ 25,000 (US $ 45,000 or Euro 35,000).
Doktor Jon believes, "The single most vital operational function for a modern Town Centre CCTV scheme, is that in the event of an incident occuring, the system must be able to provide clear identifiable evidential quality images of the suspects or vehicles involved.
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