AGC

Automatic Gain Control is an electronic circuit that amplifies the video signal when the strength of the signal falls below a certain value.

Angle of View

May be expressed in Diagonal, Horizontal or Vertical. Smaller focal lengths give a wider angle of view.

Aperture

The opening of the lens that controls the amount of light reaching the surface of the pickup device. The size of the aperture is controlled by the iris adjustment.

Aspect Ratio

The ratio of width to height for the frame of the televised picture. 4:3 for standard systems

Auto Balance

A system for detecting errors in color balance in white and black areas of the picture and automatically adjusting the white and black levels of both the red and blue signals as needed for correction.

Auto Iris Lens

A lens with an electronically controlled iris, allowing the lens to maintain one light level throughout varying light conditions.

BACK FOCUS

A mechanical adjustment in a camera that moves the imaging device relative to the lens to compensate for different back focal lengths of lenses. An important adjustment when a zoom lens is fitted.

BALUN

A transformer that levels out impedance differences, so that a signal generated on to a coaxial cable can be transferred on to a twisted pair cable.

BLACK LEVEL

The dark parts of a video signal corresponding to approximately 0.3 volts.

BLC (BACK LIGHT COMPENSATION)

A feature of modern CCD cameras, which electronically compensates for high background lighting, to give details that would normally be silhouetted.

BNC

Video connector used in CCTV installations.

Camera Format

The approximate size of a camera image pickup device. This measurement is derived from the diagonal line of a chip. Common formats are 1/6”, 1/4”, 1/3”, 2/3” and 1".

CCD

Charge coupled device, a flat thin wafer that is light sensitive and forms the imaging device of most modern cameras. Size is measured diagonally and can be 1/3"-1/2" or 2/3". There are two types, frame transfer and interline transfer.

CCIR

The European 625 line standard for the video signal.

C-Mount

An industry standard for mounting a lens to a camera with a 1" x 32 thread and a distance from the image plane of 17.52mm from the shoulder of the lens. A C-mount lens may be used with a CS-mount camera with a 5mm-adapter ring.

Coaxial Cable

A type of cable capable of passing a wide range of frequencies with very low signal loss.

Compression

The reduction in gain at one level of a picture signal with respect to the gain at another level of the same signal.

CS-Mount

An industry standard for mounting a lens to a camera with a 1" x 32 thread and a distance from the image plane of 12.52mm from the shoulder of the lens. A CS-mount lens may not be used on a C-mount camera.

Depth of Field

The in-focus range of a lens or optical system. It is measured from the distance behind an object to the distance in front of the object when the viewing lens shows the object to be in focus.

Depth of Focus

The range of sensor-to-lens distance for which the image formed by the lens is clearly focused.

Digital Signal Processing

An algorithm within the camera that digitizes data (the image). Examples include automatic compensate for backlight interference, color balance variations and corrections related to aging of electrical components or lighting. Functions such as electronic pan and zoom, image annotation, compression of the video for network transmission, feature extraction and motion compensation can be easily and inexpensively added to the camera feature set.

Distortion

The deviation of the received signal waveform from that of the original transmitted waveform.

EIA

Electronic Industries Alliance. Monochrome video signal standard used in North America and Japan: 525 lines 60Hz

Equalizer

An electronic circuit that introduces compensation for frequency discriminative effects of elements within the television system, particularly long coaxial transmission systems.

ETHERNET

The most widely used LAN transmission network. Based on a bus network topology, it runs at a maximum speed over 100 meters of 10Mbit/s. It operates over conventional co-axial cable, thin wire co-axial cable and unshielded twisted pair cabling. This has several implementations - 10Base5 for use over conventional co-axial cable, 10BaseF for use over optic fibre, and 10BaseT for use over Unshielded Twisted Pair (UTP) cabling.

Field of View

The horizontal or vertical scene size at a given length from the camera to the subject.

F-Number

Indicates the brightness of the image formed by the lens, controlled by the iris. The smaller the F-number the brighter the image.

Focal Length

The distance from the center of the lens to a plane at which point a sharp image of an object viewed at an infinite position. The focal length determines the size of the image and angle of field of view seen by the camera through the lens. This is the center of the lens to the image pickup device.

Framerate

The number of frames per second that the camera produces.

F-Stop

A term used to indicate the speed of a lens. The smaller the F-number the greater amount of light passes through the lens.

Gain

An increase in voltage or power, usually expressed in dB.

GALVANOMETRIC

This is one method used on Auto Iris and Direct Drive lenses to move the iris vanes, open and closed using a coil operation.

GAMMA CORRECTION

An electronic correction carried out by the camera circuitry to balance the brightness seen by the camera to that of the monitor.

GATEWAY

A node that allows connection to another network using another protocol.

GROUND LOOP

An alternating current (AC) that can be produced in a cable. This is usually caused by parts of the system being fed from different electrical sources resulting in different earth potentials at each end of the signal path. This results in interference of the video pictures in the form of a black shadow bar across the screen or as a tearing effect in the top comer of a picture.

GROUND LOOP TRANSFORMER

An isolation transformer. There is no direct connection between input and output.

HERTZ (Hz)

The number of variations per second (e.g. picture frames, alternating of the current, etc).

HTTP

Hyper text transfer protocol.

HTTP Port 80

Normally this is the HTTP port address that cameras can communicate over.

Impedance (input or output)

The input or output characteristic of a system component that determines the type of transmission cable to be used. Expressed in ohms.

IP Address

The network location of an IP camera, which can be located using a Web browser on a PC. (example – 192.168.1.100)

Iris

Mechanism within a lens to regulate the amount of light that passes through, and falls upon, the image sensor. It can be controlled manually or automatically.

Jitter

Small, rapid variations in a waveform due to mechanical disturbances or to changes in the characteristic of components. Supply voltages, imperfect synchronizing signals, circuits, etc.

Lens

A transparent optical component consisting of one or more pieces of optical glass with surfaces curved (usually spherical), so that they converge or diverge the transmitted rays of an object, forming a real or virtual image of that object.

Lens Format

The approximate size of a lens-projected image. In most cases the lens will project an image slightly greater than the designated image size to insure the pickup device is completely covered. It is recommended that camera and lenses are the same format size. A lens larger format size can be used on a smaller format camera, however a smaller format lens should never be used with a larger format camera.

Lens Speed

Refers to the lens aperture or its ability to transmit light. This is measured in F-stops.