By Les Simmonds.
Is CCTV complicated? Or is it perceived to be complicated because of the lack of CCTV-educated and/or trained personnel in the security industry?
In this article, we will cover various areas from the system planning and design to the installation and testing of a CCTV system and will cover most areas in between where things might go wrong and hopefully show you how easy CCTV really is!
CCTV System Planning And Design
To design an analogue or IP CCTV system for two to 10,000 or more cameras, the following basic steps should be considered:
Step one: Do you need a CCTV system? Maybe all you need is a padlock or a fence. Too many people just want a CCTV system without due consideration of the reasons why it might be needed.
Step two: Decide the purpose of the CCTV system. Will your system be actively monitored or a forensic system? Will your system cover several sites and what are the different requirements between the sites? Is a network or communications between multiple sites in place or required? It is important at this stage to remember that CCTV systems are not security systems on their own. Will your CCTV system be integrated into security technologies and if so, how? How will the whole system be controlled – from one control centre, or from several control centres? Will your control be old-fashioned push buttons, or a smart software-based video-management system (VMS)?
Step three: Work out the areas to be viewed by each camera and the type of camera required for lighting conditions, environment and position. Is additional lighting required? Is ‘pan tilt zoom’ required for any camera? Will the cameras be PAL (SD), 720p, 1080p, or megapixel in format?
The total individual screen image height for identification (taking loss of sharpness due to normal levels of video compression into account) would be 100 per cent for PAL (SD), 70 per cent for 720p and 50 per cent for 1080p. Megapixel cameras may be any height due to vertical pixel count and aspect ratio. Using an HD 1080p camera, a quality lens and a correctly laid out and lensed system design, it will be possible to achieve identification of individuals with only 50 per cent screen height compared with 100 per cent screen height specified in the current Australian CCTV Standard AS 4806.2006: Part 2 clause 3.7 for PAL (SD) cameras.
Step four: Consider privacy and workplace surveillance issues and relevant legislation.
Step five: Decide your monitoring requirements, such as quantity, layout and location of monitors. Will there be any sub control rooms or remote control rooms? Will the monitors be held in black until an alarm-activated event? Operator-to-monitor viewing distance should comply with occupational health and safety requirements. Your monitoring and control requirements determine the VMS configuration. Determine the video and data storage requirements and set the storage capacity to suit.
Step six: Use equipment that complies with your site requirements and your site equipment tests, or is known by you to have the required operating parameters. Note that equipment specifications can only be considered as a guide. Equipment performance and compatibility at your site, under your site conditions, is all that really matters. So do not be afraid to carry out CCTV equipment comparisons at your site, under your conditions.
It is important to create, develop and expand your own checklist for each of the above sections. This will allow you to develop your own procedures and fine-tune as you use them. Then you will be surprised at how easy it will be to plan a CCTV system.
The above CCTV system planning and design process is basic and will not be complicated to anyone with a basic CCTV understanding or CCTV education and/or training.
CCTV Lenses
No write-up about CCTV being perceived as complicated can get by without mentioning lenses. Lenses are the single most common item misunderstood by the security and IT industries. IT companies are becoming big CCTV players but there is no reason for the lack of understanding other than a lack of interest, education or training.
Lenses are probably the most underrated and mysterious item in the CCTV chain. All CCTV system images pass through a lens and yet the importance of the lens to the whole system is often overlooked.
There are many lens selection aids available these days; there are complex formulas and the most common selection aids are available from most reputable lens manufacturers.
When you look at the table below you will see there is a pattern emerging for the most common CCTV camera chip formats with the most common-sized fixed lenses.
The horizontal angle of view in degrees in the table are approximate but suitable for most CCTV applications.
The horizontal angle of view of 30, 60, and 90 degrees represent more than 90 per cent of all fixed lens applications and all can easily be considered by using or thinking of the common 30- 60- or 90-degree setsquare that we have all used at some time in our life. These three angles are easy to remember and if you need to show approximate angles of view on a plan, you can purchase a setsquare at your local newsagent to mark up the plan.
In many cases the vertical angle of view also has to be considered and if the aspect ratio is 4:3 this means that the horizontal is 4 units wide and the vertical is 3 units high. Therefore, the vertical angle of view with this aspect ratio is 75 per cent of the horizontal angle of view and is easily calculated.
If the aspect ratio is 16:9 this means that the horizontal is 16 units wide and the vertical is 9 units high. Therefore, the vertical angle of view with this aspect ratio is 56.25 per cent of the horizontal angle of view and is reasonably easy to calculate.
The lens calculation shown above is very simple. Once you use it a few times it is with you all the time and will not let you down.
Now that you have the most simple lens calculation methodology for common fixed lenses available, there are other lens issues that need to be considered, such as:
- Lens formats: Will the lens match or suit the camera sensor?
- What will the lens speed (f-stop maximum and minimum) be?
- What is the required depth of field?
- Will you use a manual iris, auto iris or motorised iris?
- Will the selected lens and camera combination handle the lighting dynamic range?
- Will you use glass, plastic or cola-bottle quality lenses?
Another easy method for field lens size calculation is a simple geometry formula, where the lenses are the common 60- or 30-degree horizontal view lenses. See the table overleaf for the relative lenses sizes with 1/2”, 1/3” and 1/4” camera chip formats.
A 60-degree lens will show the same scene width as the distance from the object and a 30-degree lens will show half the scene width as the distance from the object.
An example would be: if the camera/lens combination is 20m from a wall, a 60-degree horizontal view lens will show a horizontal view which is 20m wide on the wall. This formula applies to all 60-degree horizontal view lenses and as the distance from the object changes, so will the width of the horizontal view. For example, if the camera/lens combination is 10m from a wall, a 60-degree horizontal view lens will show a horizontal view, which is 10m wide on
the wall.
A 30-degree horizontal view lens such as those shown in the table would show half the horizontal view on the same wall with the same distance as the previous 60-degree calculation. An example would be: if the camera/lens combination is 20m from a wall, a 30-degree horizontal view lens will show a horizontal view, which is 10m wide on the wall. If the camera/lens combination is 10m from a wall, a 30-degree horizontal view lens will show a horizontal view, which is 5m wide on the wall.
The simple angle-of-view formulas given here are approximate and are more than adequate for most CCTV applications and they should allow you to satisfy the most important thing – your client’s requirements.
The above CCTV lens information will not be complicated to anyone with some CCTV education. What do you think?
Les Simmonds is an independent CCTV consultant; he is also a fully qualified broadcast television and radio professional and a graduate of RMIT and ABC TV Australia. Les has been involved in closed circuit television (CCTV) technologies since 1982 and is one of the leading innovative CCTV consultants in Australia.
Les is Chairman of the Standards Australia Non Broadcast Television Committee, which has subcommittees for CCTV, Medical Video, Industrial Video, Professional Camcorders, Consumer Camcorders and a Non Broadcast Video Testing. Les can be contacted by email at les@cctvconsultants.com.au.
More comprehensive information is available at: www.cctvconsultants.com.au/index.html and www.cctvconsultants.com.au/about.html.
