Guide to CCTV Cameras
Of course you can’t have a CCTV System without cameras! However, there is a lot more to surveillance cameras than most people think. And having the right camera is essential for an effective system.
Think of a CCTV camera as an eye. Just like an eye, light enters the camera through a lens. In an eye, the light then hits the retina which sends signals to the brain. In a camera, it strikes an electronic sensor which turns the image into an electronic signal. An electronic processor known as a “chipset” (sometimes referred to as a DSP acts as the brain and processes this signal).
Definition & Resolution
Typically, the image quality of most modern surveillance systems is referred to in terms of definition (High Definition, Full High Definition etc.) and is measured in Mega Pixels (MP). Older analogue technology systems image quality of cameras is measured in Television Lines or TVL. The higher the Mega Pixel or TVL, the higher the image quality.
But before you go rushing off to buy a 4MP Full High Definition camera because the salesman has told you it is the best thing since the invention of sliced bread – wait a minute! No amount of resolution will give you the image you want without the use of the correct camera lens. For example, you will not be able to effectively identify a person at 50m range with a 3.6mm wide angle lens. The person will just be too small due to the wide field of view.
In other words, don't get caught out by
someone telling you the camera will give your exceptional surveillance just
because it is a 3MP or 4MP camera. You need to also consider what lens will be
Analogue High Definition & HD-SDi
Many customers want to upgrade existing systems to High Definition or Full High Definition but find the cost of having to replace cables too expensive. This is only necessary if installing an IP based system. Thankfully there is now AHD and HD-SDi as we as a number of other options. These technologies allow people to upgrade to HD or FHD without having to upgrade their cable infrastructure.
This should be the first consideration when buying a CCTV system!
Measured in millimeters, it is the focal length of the lens. The larger the number, the narrower is the field of view, which in turn relates to the “zoom” or telephoto the lens will deliver and the more detailed the object under surveillance.
For example, a 3.6mm or 4mm lens can be considered a wide lens and a 12mm lens more zoom. Simply put, a wide angle lens will provide greater coverage of an area under surveillance, but the detail will be limited due to the size of image. On the other hand, a lens with more zoom will show more detail but the overall coverage will be less.
Varifocal Camera Lens
Many cameras are now available with a varifocal lens. Basically, this is a manual zoom lens.
Cameras with varifocal lens may cost a few dollars more than a fixed lens, but you will generally be far better off buying one unless you know exactly what size fix lens would best be suited to your application. This is because you can zoom in and out to fit exactly the image you want. It is also useful in the event that you change the camera position or redirect the camera.
DIY CCTV Camera Packages
With availability of CCTV products now available in retail outlets and on EBay it is no wonder that many people see this as a cheap option when buying a CCTV system. The trouble is, they often find that the supplier’s claims are not quite what they seem. Yes, this includes the resolution of the cameras. Some manufacturers will show “comparison” images. But it is not unknown for companies to use high quality “still” photographic cameras to show a deceptively clear image. There are many other issues also, the least of which is the stability and reliability of the product. These and many other issues will become clear as you read further into this article.
Most CCTV cameras use one of two types of sensor – CMOS or CCD.
CMOS sensors are a cheaper sensor. Although very common, but do not give a very clear image unless the camera has additional processing to enhance the image. The big benefit of CMOS is the cheaper cost.
On the other hand, CCD sensors (short for charge coupled device) are more expensive, but the image quality is usually far higher than that of CMOS. They also need less additional processing. CCD is the preferred sensor for most professional CCTV cameras.
1/4 inch or 1/3 inch CCD Sensor - why 1/3 inch is better
Typically, cameras are available with either 1/4” or 1/3” CCD or CMOS sensors. This is the physical size of the sensor. The size of the sensor determines the cameras sensitivity to light. Smaller sensors are also more prone to “noise”. It is therefore advisable to use a camera with the larger 1/3” sensor, especially if buying a cheaper product which may have a poorer quality DSP.
DSP or “Chipset”
If the sensor is the heart of the camera, then the DSP or “chipset” is the brain. This component is responsible for enabling the cameras to operate in varying light levels, including low light levels and conditions. It is therefore correct to say that the better quality of the chipset, the better the cameras ability to operate in various conditions.
However, you should also be aware that many cheaper cameras, particularly those offered on websites such as Ebay use “non-genuine” components such as chipsets and sensors. They remove the original details and replace them with names such as Sony or Panasonic.
This is a very important consideration when purchasing a CCTV system. Light levels are measured in Lux. Basically, 1 Lux is equal to 1 candle at 1m.
In the case of CCTV it refers to the amount of light required for the camera to operate effectively. The lower the Lux number, the lower the light level the camera will operate in. Most professional cameras will operate in light levels of just 0.001Lux or even lower.
Infrared Night Vision
Many camera are now equipped with infrared illuminators. These provide light which cannot be seen with the naked eye, but can be seen by the camera. Depending on the camera and the type of illuminators, they can provide illumination ranging from 10m to over 250m.
Most IR camera will display a slight reddish glow from the illuminators in the dark. However, new "Black" LED technology results in no glow.