Activity Detection: A feature of the video multiplexer range that uses video motion detection techniques to improve the camera update times.

Alarming: The ability of CCTV equipment to respond to an input signal, normally a simple contact closure. The response varies depending on equipment type. Many cameras have alarming functions built-in; however, most CCTV installations today use the DVR as a central monitoring of motion and alarm responses.

A.L.C. (Automatic Level Control): On AI lenses, also known as the peak/average control. Adjusting this control allows the auto iris circuitry to either take bright spots more into consideration (peak), bringing out detail in bright areas, or less into consideration (average) bringing out

Analog: A signal in which any level is represented by a directly proportional voltage; not digital.

Angle of view: The angular range that can be focused with a given lens. Small focal lengths give a wide angle of view, and large focal lengths give a narrow field of view. A 3.0 mm lens and lower is considered a wide angle lens.

Aperture: The opening of a camera lens that controls the amount of light reaching the surface of the pickup device (CCD). The size of the aperture is controlled by the iris adjustment. By increasing the f stop number (f1.4, f1.8, f2.8, etc.) less light is permitted to pass to the pickup device.

Aspect ratio: The ratio of the picture frame width to the picture frame height in standard broadcast TV systems. It is typically 4 units horizontal over 3 units vertical or a 4:3 ratio.

Aspherical Lens: A lens with a non-spherical shape refracts the light passing through it. It is typically used on wide angle lenses to decrease distortion or fisheye effect or it is used to allow more light to pass by lowering the lens aperture

Attenuation: A decrease or loss in a signal. The longer a cable extends, the more attenuation, or weaker signal occurs.

Automatic Frequency Control (AFC): An electronic circuit used whereby the frequency of an oscillator is automatically maintained within specified limits.

Automatic gain control (AGC): A feature that is used to automatically adjust the signal strength based on certain parameters based on the signal input and other specified parameter. Found on many DVRs.

Auto Iris lens: A lens in which the aperture automatically opens or closes to maintain proper light levels on the camera pickup device (CCD). This function allows the lens to automatically adjust to lighting conditions. Used in all outdoor cameras and many indoor with outside reflecting light or changing ambient light levels.

Automatic Level Control (A.L.C.): A feature on Auto iris lenses (also known as the peak/average control). This allows the Auto Iris lens to either take bright spots more into consideration (peak), that allows detail in bright areas, or less into consideration (average) bringing out detail of shadows or darker areas of the picture view.

Auto-Terminating: Feature whereby the equipment automatically selects the correct termination depending on whether the video output BNC is connected.

Auto White Balance: A feature on many color cameras that monitors the light and adjusts its color to maintain the light areas.

BNC: British Naval Connector. A trivia question somewhere. The traditional CCTV camera termination method. BNC connectors come in twist-on or crimped connections.

Back focal distance: There is a mechanical back focal distance -The distance from the flange of the lens (beginning of the lens mount) to the focal plane. C-mount lenses have a flange back distance of 17.526mm vs. 12.5mm for CS-mount. Optical back focal distance is the distance from the rear most portion of the lens glass to the image plane. .

Back Light Compensation (B.L.C.): A feature on professional CCTV cameras which electronically compensates for high background lighting to give detail which would normally be silhouetted. It allows adjustment to compensate for shadows and dark areas in the camera view.

Bandwidth: A measure of the load and capacity of information over a network. Video transmission takes more bandwidth to transmit over a network than text.

Black level: The video signal level that corresponds to the maximum limits of the black areas of the picture.