CCTV System Components, Cameras, Lenses, and Signal Transmission
The signal chain
Every CCTV system follows the same chain: scene → lens → image sensor → processor → transmission → recorder → display. A fault anywhere breaks the picture, so diagnose in order rather than guessing. Know the main camera types: fixed, pan-tilt-zoom (PTZ), dome (discreet, vandal-resistant), bullet (directional, obvious deterrent), and multi-sensor units. Understand resolution (pixels), frame rate (fps), bit rate, and how compression (H.264/H.265) trades quality for storage.
Lenses and light
Key lens ideas: focal length (short = wide field of view, long = narrow and detailed), varifocal lenses, aperture/iris and depth of field, and infrared (IR) cut filters for day/night. Understand lux (light level), WDR (wide dynamic range) for bright-background scenes, and why IR illuminators produce washed-out faces at close range.
Transmission
Analogue systems use coax and are prone to interference over distance; IP systems use Ethernet and switches, with PoE carrying power and data on one cable. Watch for bandwidth limits, network latency, UPS backup, and cyber-security (default passwords, unpatched firmware).
Traps
Questions swap focal length with field of view direction, confuse frame rate with resolution, or suggest that a higher megapixel count always improves identification - it does not if the face occupies too few pixels.
Rule of thumb
For identification, the face should span roughly 40–50 pixels between the eyes; for recognition, about 80–120 pixels is a safer planning figure. If the subject is smaller than that, you have detection, not identification.
Worked example
A wide shot shows a person at the far end of a car park. The operator zooms in digitally and claims identification. Correct answer: digital zoom adds no detail; only optical zoom or a closer camera improves pixel density. Report the subject as "detected, not identified."