Focal length is the distance between the lens' optical center and the sensor recording the image. It is measured in millimeters (mm).
This length measures the visual system's strength in converging or diverging light. The positive value of the focal length shows the light convergence, while a negative value highlights its divergence. While determining the focal length, the camera's focus must be to infinity.
In simple terms, it defines the angle of view your camera will cover and the size of the individual elements in a picture (magnification).
The shorter the focal length value, the wider the coverage area will be. Such a lens is known as a wide-angle lens. In this case, the lens bends the light sharply. It means the camera with a lower focal length will show more area of a scene. Similarly, the camera with a higher focal length will have narrow area.
The physical size of a longer focal length lens is larger. So, you can use this feature as a mark to estimate the lens type used in your CCTV Cameras.
Moreover, the focal length impacts the perspective of the picture taken from a particular camera. You'll find more space within the elements of the scenes with a shorter focal length or wide lens, often termed view expansion or zoomed out. However, it is the opposite in the longer focal lens, where the end results seem to zoom in.
Also, an impact of focal length can be seen on the image quality. Any vibration in the CCTV will likely impact the pictures with long focal lengths. These lenses are highly motion-sensitive and can often cause blurriness.
Ultra wide angle, standard wide-angle, standard lens, and telephoto lens are the primary lens type based on focal length differences. The proper camera selection for security depends on the area under consideration, your priorities, and your budget.