There are a number of important factors to consider when purchasing a new CCTV camera, most of which map to one or more of the basic hardware components, so understanding the components and how they affect the CCTV camera’s performance is an important part of knowing what to look for.
Choosing the Right Lens
The lens is what gathers the light for the sensor. Everything the viewer sees, or that gets recorded on the DVR comes through the lens. It determines the distance at which a car’s number plate can be read, and a face can be recognised because the lens controls focus. In many cases, a better lens is more helpful than a higher output resolution, as the output is always limited by the input, and the lens determines the input.
Buyers should also look for a zoom lens. Some CCTV cameras come with digital zoom, where others have optical zoom, handled by the lens. Whenever possible, buyers should opt for optical over digital zoom. The problem with digital zoom is that it provides no more information than was in the original image. Optical zoom can actually add new information as it changes which light reaches the sensor.
Choosing the Right Sensor
Not all digital sensors are created equal. There are two main things to look for when studying the sensor specifications of a given CCTV camera: the first is the sensor type, the second is the sensor size. Most CCTV sensors are either CMOS or CCD. CMOS is less expensive and uses less power than CCD, but it is less sensitive and does not produce as clear an image, which can be particularly problematic when using the camera for identification purposes. One result of this is that CMOS-based sensors require more signal processing to produce a clear image.
The other important factor is the sensor size. The larger the sensor, the more light it can process, and the higher quality image it can produce. Most CCTV camera sensors come in one of two sizes: 1/4 inch, which measures 3.2 mm by 2.4 mm, and 1/3 inch, which measures 4.8 mm by 3.6 mm; giving it over twice the surface area of the smaller sensor. A larger sensor not only gathers more light, but in doing so gives the DSP more data to work with, which is especially helpful with the less capable processors used in budget cameras.
Choosing the Right Output Resolution
One very common specification for CCTV cameras is the number of horizontal lines of TV resolution it can output, or its TVL. This can range anywhere up to 700TVL, with many cameras coming in between 380TVL and 540TVL. Some experts recommend 420TVL as a minimum, but this is not always the case. While a high resolution is nice to have, the output depends on the input, so if the lens and sensor cannot match the output resolution, which is determined by the DSP, then the extra resolution is wasted. What matters most is having enough resolution to clearly display any image the camera can produce. Anything beyond that is unnecessary.