The first step in selecting your CCTV system is to write down exactly what you wish this CCTV system to do. Here are some typical things to decide:
1. Will you be monitoring the targets from an external location or not. In other words, will you require an Internet connection to your CCTV system? If you wish to view the outputs of cameras remotely, then you will almost certainly require a high speed Internet connection because a single camera shot contains a lot of data and this will take too long to transmit over dialup Internet connections.
2. What areas will you need to cover?
3. Where will you locate the non-camera equipment and does it have to be very secure? For example, if you are using the system to monitor break-ins, you will be out of luck if the burglar steals the DVR with all of the photographic evidence about his break-in.
4. Can you use fixed cameras or must they be able to move and, if so, who will operate them? (Note that most CCTV systems do not have a dedicated operator such as a security guard and use fixed position cameras.)
5. Will you be using this system to gather information that will be used by the police for things such as property damage or shop lifting? If so, then you will require a DVR with the ability to make watermarked DVD/CD copies.
6. Do you even need to keep a copy of the camera pictures for your own records? If not, then you may not require a DVR, only monitors.
7. Will you need to install cameras in a remote location, such as a detached garage, to which it will be very difficult to run signal wires? If so, then you need to consider wireless cameras and receivers.
8. Will you need to monitor activities under dark or semi-dark conditions? If so, then you will probably need IR cameras. Be careful that the camera being used under these conditions does not have to look through a piece of glass. If this is the case, then you will need a special, low light camera as the infrared LEDs on the front of the camera do not work well through glass because of reflections.
9. Do you need to:
a. Recognize only that known people are present and occasionally move, i.e. that employees are present and not sleeping?
b. Identify known people. For example, which employee entered a storeroom?
c. Identify unknown people such as burglars or shoplifters?
10. Who will install your system? Almost of the wiring involved is low voltage wiring and so it is usually not a problem to install it without a licensed electrician unless you need additional power outlets to power things such as the monitors and DVR. However, this installation may be covered by local laws and ordinances and it is your responsible to ensure that you are in compliance with same.
11. Who will run and maintain your system and how much training will they require?
12. In the event of a power failure, how long will your system need to operate? To operate in the event of a power failure will require a UPS or some other backup power arrangement.
13. Will you need to install an independent alarm system in order to satisfy your security requirements? Perhaps you already have one.
14. Are their any special environmental considerations that require special camera housings? Examples would include such things as:
a. Icing because the camera is outside in an unsheltered location.
b. The presence of explosive or flammable dusts or fumes such as a paint booth, gas station, or woodshop.
c. Grease buildup from a nearby restaurant kitchen.
15. What is your budget for this project? There will be physical installation labor costs, setup costs, and the actual hardware costs. Note that some decisions made above can be very expensive.
The next step is to make a scale drawing of the area that you wish to cover with the CCTV cameras, including remote buildings. Identify where you will place the DVR (if required), any monitors, and the location of your Internet access. Cameras that are wired back to the monitoring point can be powered via the signal cable and so there is no requirement for a local power outlet near the camera. In addition, your local laws and ordinances may prohibit cameras in certain locations such as restrooms and other locations where people may have an expectation of privacy. It is your responsibility to ensure that you are in compliance with all such restrictions including, but not limited to, posting signs informing people that they are being recorded.
Unless you have experience in the matter of selecting suitable CCTV equipment, it is strongly recommended that you contact your supplier with the above information for assistance in selecting the appropriate materials. If not, you might get lucky but it is more likely that you will probably end up with some expensive extra equipment that you might wish to sell on E-BAY.
All of the following information depends greatly on the resolution of the camera involved, its orientation, and the associated recording device. These rules of thumb are appropriate for cameras having approximately 420 lines of resolution to about 540 lines of resolution. When you go to the higher resolution IP cameras, then the above rules can be relaxed but the individual component costs start to increase fairly quickly. There are three general rules of thumb for selecting lenses:
1. To see that a person is present, the person’s image should fill at least 10% of the display height.
2. To identify a known person, this person’s image should fill at least ¾ of the display height.
3. To identify an unknown person, this person’s image should fill somewhat more than the display height.
If you have a small business and just wish to see if your employees are present without necessarily being able to specifically identify them, then a wide angle lens, such as a 2.8 mm focal length is appropriate and only one or two cameras will probably be required. Assuming that the store is well lighted, then no infrared LEDs on the camera are required. However, care must be taken to arrange the cameras so that they do not directly view the outside through windows or open doors as this will upset the quality of the picture during the day. The camera will try to adjust the picture level for the bright light coming in from outside thereby rendering the interior parts of the image too dark. This outside light condition may require additional cameras and then, a longer focal length lens might be appropriate. However, if you wish this system to do dual purpose as to also identify a break-in, then the problem becomes much more complex. Also remember that people involved in a break-in or theft may be able to hide their faces making it nearly impossible to establish their identity. Even a professionally designed CCTV system cannot solve this problem.
For any application involving records that may be presented for legal purposes, it is essential that you have your CCTV system designed by an appropriate technical expert and the images must be watermarked in the DVR. What this means is that there is an invisible signature buried in the image that will be distorted if the image is edited after it is taken.
Table 1 presents some approximate field of views for different focal length lenses. The camera is tilted down at differing angles in order to maximize the probability of recognizing a person in the field of view. The distances given are horizontal distances from the camera, not the slant distances. The empty cells in the table represent locations where the camera cannot see the ground at that horizontal distance. Note that at a distance of 50 feet, the camera will only be seeing the ground and nothing above it.
A good supplier can provide documentation on what your system should see with selected components. However, as preparation of this documentation requires a significant amount of work, a non-refundable deposit may be required. If you purchase the equipment from the supplier in question, then most, if not all, of the deposit can be applied towards your equipment purchase. However, this is a function of the supplier’s corporate policy and many suppliers cannot provide this function. Figure 1 below shows a typical camera view for a specified lens and camera mounting height. The distances shown are in feet and the lens has a 4 mm focal length. With some additional work, a 3D drawing can also be produced given the room dimensions and window and door sizes and locations.
All lenses have a certain tolerance on the focal length. In other words, a 4 mm focal lens may actually be say 3.8 mm. Hence, for critical applications where it is necessary to have an exact focal length lens, it may be necessary to use a VARI-FOCAL lens, i.e. one that has an adjustable focal length. Usually, however, this is not necessary.
