Analog CCTV Cameras
Analog CCTV cameras are available in a wide variety of formats and performance specifications.
Cameras are the starting point of the video signal and are therefore a critical component of a CCTV system. A variety of analog camera types are available including monochrome, colour, colour/mono (day/night), cameras sensitive to infra-red light and thermal cameras. Cameras are available in different physical formats e.g. standard box camera, printed circuit board (pcb) camera. The camera itself may be mounted in different formats of housing to protect it from a variety of environments from dust, rain, heat, explosion and radiation.
Camera Specifications
Cameras can be specified and compared using a number of specifications shown like resolution, sensitivity, signal to noise ratio, camera voltage, chip type, and operating temperature.
Resolution
Resolution is the quality of definition and clarity of a picture and is defined in lines
More lines = higher resolution = better picture quality.
Resolution depends upon the number of pixels (picture elements) in the CCD chip. If a camera manufacturer can put in more number of pixels in the same size CCD chip, that camera will have more resolution. In other words the resolution is directly proportional to the number of pixels in the CCD chip.
Horizontal Resolution
Horizontal resolution = no. of vertical lines
Theoretically horizontal resolution can be increased infinitely, but the following two factors limit this. It may not be technological possible to increase the number of pixels in a chip. As the number of pixels increase in the chip, the pixel size reduces which affects the sensitivity. There is a trade off between resolution and sensitivity.
Typical Resolutions of Cameras
| Monochrome Cameras | Colour Cameras | |
|---|---|---|
| Low Resolution | 380 - 420 lines | 330 lines |
| High Resolution | 570 lines | 540 lines |
Sensitivity
Sensitivity measured in lux indicates the minimum light level required to obtain an acceptable video picture. Minimum scene illumination indicates the minimum light required at the scene to get an acceptable video picture.
Wavelength Response
Standard analog cameras will be sensitive to visible light (approx. 400-700nm). Some cameras have sensitivity in the near infra-red light range (700-1000nm) which makes them suitable for use with CCTV infra-red (IR) lighting. IR lamps used in CCTV typically have a wavelength characteristic of 715nm (visible), 830nm (difficult to see with the human eye) or 950nm (black "invisible").