CCTV glossary

Colour vs mono

Black and White cameras can operate in lower lighting conditions than colour, so there are decisions to be made. Colour works well in many internal locations or in a well lit external environment. Cameras can come as mono-only, colour-only or can have the ability to switch automatically from one mode to the other as lighting conditions change (day/night cameras). It is also possible to use invisible infra red illumination with some mono cameras, if white light is not suitable.

Resolution

Medium Resolution is the description usually applied to cameras with 380 lines, mono or colour. High Resolution describes cameras with 560 lines mono or 460 lines colour.

Field of view

Just like some people, cameras can suffer tunnel vision. Those with a fixed field of view are referred to as Fixed Cameras. Fully functional devices can select both the field of view and the depth of view (Speed Domes and Pan & Tilt cameras).

Camera configuration

Cameras can look just like a traditional video camera, where visibility of the device could act as a deterrent. Dome style cameras are more discrete and make it difficult for miscreants to know what is being filmed. Externally mounted cameras should be designed to be weather resistant. There is an industry standard for measuring how waterproof they are, known as an IP Rating. IP65 or, better still, IP66 should be the minimum standard you should consider.

Camera lens

There are three main groups. Manual Iris lenses, once installed, cannot accommodate wide variations in brightness. Image quality is adversely affected by sunlight or bright lights. Auto Iris (AI) and Direct Drive (DD) lenses work much more
like the human eye. They are the preferred lenses where ambient light levels change and a must when viewing things like doorways.

Control equipment

The control equipment is used to link cameras to the monitor and the recorder. Manual/Auto switch devices are basic ways of connecting a number of cameras. They will allow the monitor to view only one camera at a time and only that view will be recorded. Multiplex control equipment is much more comprehensive and is the preferred option. There are two approaches - Simplex or Duplex. Simplex devices record all cameras simultaneously, and each one can be viewed in turn. If the operator chooses to view a multi-screen image on monitor, Simplex devices can no longer record from more than one camera. Duplex controllers go that one step further - recording from a number of cameras, irrespective of whether the operator is taking a single view or a multiscreen view on the monitor.

Recording equipment

The two main approaches to recording are Analogue (videotape) and Digital (on PC or hard disk storage). Analogue - in use for many years, runs on special VHS or Super VHS machines that can record from more than one camera at a time. ‘Time Lapse’ is the practice of recording for a set period, usually 24 hours, when the tape is replaced and stored off-line. It is customary to use a tape no more than 12 times a year before it is securely destroyed. Allowing one tape for each day of the year means 31 tapes are involved in the cycle. Digital image recording – far superior in image quality, is a more secure medium. Security and image integrity are essential if recordings are to be used for police and Crown Prosecution Service evidence. Digital devices can be standalone, replacing existing multiplex controllers, or can be networked (including internet access for secure interrogation and control). As with computer systems, it is essential that your supplier understands the implications of image storage capacity and the rate of image capture and confirms they are more than adequate.

Data protection

To comply with Data Protection legislation, you will need to register any CCTV system that records and stores information on others’ actions. You can get details from the web at www.dataprotection.gov.uk. Essentially, you are required to implement a data management system that records the custodian of the data together with details of everyone who is authorised to change tapes or download data. Uncontrolled data, as well as falling foul of the Data Protection Act, will not stand up in court. You should also ensure your supplier designs a system that does not contravene legal requirements or local by-laws (such as those affecting cameras overlooking public places). Areas used by children, such as schools or recreation areas, are particularly sensitive.

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