Some time ago we issued guidelines for the identification of persons and vehicles. This is fine, but many system engineers were trying to find what camera and lens combination will satisfy these identification guidelines. And what about end users who know even less about camera and lens formats, how can they understand the competing specifications? This article all will be revealed for both groups. 

In this Charts we will try to show the horizontal and vertical fields of view for many lenses and four formats are given in ‘The Principles of CCTV’ and were published in the first article CCTV. These charts also show the % of the screen height of a 5-6 feet person. The DVRMaster guidelines had not been published for general use.

The values for different degrees of identification are given as the percentage the 5 feet figure would occupy of the monitor screen. we call this the ‘screen height ratio’. The complete guidelines are provided in several DVRMaster articles and so only the basic ratios are given in this article. 

These criteria are now becoming increasingly used as part of the specification for many CCTV and security camera systems. Usually the specification will state the distance from the camera for each criterion, sometimes the specification will ask the question, ‘at what distances from the camera will the criteria apply’? In either case it involves calculations that are not too difficult but can be tedious to keep repeating for each lens and camera location. 

Another problem that many installer find difficulty in resolving are the different fields of view obtained from various camera and lenses sizes, i.e. what is the result of fitting a 1/3″ lens onto a 1/2″ camera, and how does this affect the screen height ratio at certain distances?

Here are some visual example for security camera field of view.

The effectiveness of CCTV are announced regularly. police in across the country recently claimed a drop in crime following the installation of a closed circuit TV system in the country. Not only are people delighted because they are no longer afraid to go out shopping, say local police, but even criminals welcome the chance to prove their innocence by calling on evidence from the security cameras. Crime in car parks has dropped by fifty per cent where camera exist. People say they feel safer. Indeed they should. Assaults and other violent crimes appear also to have been decimated in the center of town.

The logic, and the statistics, are superficially impressive, but some analysts are not convinced. In a report on the impact of CCTV,

The crime reduction claims being made by CCTV proponents are not convincing. Three recent criminological reports have discredited the conventional wisdom about the cameras effectiveness. In a report to the Scottish Office on the impact of CCTV.

The crime statistics rarely, if ever, reflect the hypothesis that CCTV merely displaces criminal activity to areas outside the range of the cameras. One of the features of current surveillance practice is that the cameras are often installed in high-rent commercial areas. Crime may be merely pushed from high value commercial areas into low rent residential areas. Councils often find that it is impossible to resist demands for such systems. There is an additional element of displacement that should be of particularly concern to all communities. Since the growth of CCTV as the primary means of crime prevention, more traditional, community based measures have been discarded.

A  report on CCTV in Airdre was unable to rule out displacement as a factor. 5 while various studies in other countries indicate that burglars and other criminals will travel long distances to commit crimes. 6 Discussing the justification for establishing a surveillance system of 16 cameras in Manchester,

In other words, crime may be merely pushed from high value commercial areas into low rent residential areas. One of the features of current surveillance practice is that the cameras are often installed in high-rent commercial areas. Councils often find that it is impossible to resist demands for such systems. The trend is fueled in part by the insurance industry, which in some towns is offering a thirty per cent reduction in premiums to local retailers who pay a contribution to a CCTV levy system. A nationwide insurance discount scheme is currently being negotiated, and should be in place by 2007.

Some police also concede that CCTV displaces crime. Richard Thomas, Acting Deputy Chief Constable for Gwent, recently told the BBC’s Andrew Neil that he believed CCTV pushed some crime beyond the range of the cameras. 8 And in his interview with 20/20, Leslie Sharp said “Certainly the crime goes somewhere. I don’t believe that just because you’ve got cameras in a city center that everyone says ‘Oh well, we’re going to give up crime and get a job”.

The cameras are also creating a vastly increased rate of conviction after crimes are detected. Virtually everyone caught committing an offense on camera pleads guilty nowadays. Once people know they have been videotaped, they admit the offense immediately. Such is also the case in Newcastle, where the installation in 1992 of a 16 camera system has resulted in a 100 per cent incidence of guilty pleas. 9 Police are delighted at the time and money they are saving from long and expensive trials. Some legal experts are a little more wary of the implications of these results, arguing that - like DNA evidence - juries can be seduced and defendants intimidated in equal proportions by evidence that might not normally stand up to scrutiny. Indeed some districts are now reporting that people are surrendering after the mere mention in newspaper reports that their alleged activities had been captured on CCTV. 10