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How efficient are your Video Surveillance Cameras?
In order to get the best out of a security camera, it needs to be fitted with the correct lens, and placed in the most appropriate location. In the real world, that doesn't mean that it's fitted in the most convenient place for the user, or the easiest location for the installer.
It should always be considered a priority to establish the location for the camera, which provides the most effective and efficient degree of coverage, that is capable of fulfilling most if not all of the Operational Objectives. Unfortunately in recent years, there has been an industry driven encouragement towards fitting basic 'plug and play' dome or 'bullet' type cameras, many of which are highly inappropriate for their intended purposes.
Why so?, well most have barrel type lenses that cannot easily be replaced; the majority are fixed view so it's not possible to zoom in and frame the image accurately, and particularly with lower cost devices ( at least they are when they leave the factory!), the lenses fitted are equipped with a fixed iris, and are generally of an inferior quality to most interchangeable optics.
Also of course, some cameras are fitted with infra red LED's which can have the avoidable byproduct of significantly degrading the images under certain night conditions. In reality, there are some good dome and bullet cameras which produce very good pictures, and if used appropriately are a useful tool in the box; but as so often happens, many installers buy the easiest camera to fit, and they are not always the most effective in fulfilling the Operational Objectives.
Camera design aside, the same principles apply to all imaging devices, in terms of placement in relation to target identification, the only exception perhaps being ANPR license plate recognition cameras, which should never be placed absolutely head on to an oncoming vehicle ( headlights will generally wreak havoc with the image).
In most situations, an effective "Golden Zone" for target recognition will be produced when a camera is tilted between 5 and 20 degrees below the horizontal.
In general terms, the object of the exercise is to try and place a camera as close as possible to the centre line (axis) of travel for any given target, whether it be a human, vehicle or other object of interest.
In terms of camera placement relative to a target's direction of travel, the "Golden Zone" for recognition in most situations should be achieved when a camera is between 10 and 20 degrees offset from the target's general axis of movement (see diagram above).
Elsewhere on this site, you can find more detailed information on the concept of a "Cone of Containment" to help limit the coverage of lenses, and in so doing, maintain the size of targets as they move around on screen.
Please Note: The diagrams showing lens angles are intended for illustrative purposes, and are not a guarantee of accuracy or suitability for every individual situation.
UPDATE - April 2015 sees the introduction of a CCTV User's VIPER ( Video Image Performance Evaluation Report ) camera test documents, available from the TRUSTED© CCTV E-Store
In this respect, it's then relatively easy to restrict the camera's lens angle to as narrow as possible, rather than as wide as possible which is what tends to happen with the majority of installations (usually with the camera placed at too high a level).
Too often, end users think that covering the largest area is good, whereas in reality nothing could really be further from the truth.
The lens angle should always be kept to the absolute minimum needed to fulfil the Operational Objectives, and thereby minimise the "Cone of Containment"
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Doktor Jon's Guidance on .. Establishing appropriate CCTV camera angles - original content August 2008 - updated 10th April 2015
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