| ADC |
|---|
| Analogue to digital converter. |
| AGC |
|---|
| Automatic gain control- electronic Circuitry to increase the video signal in low light conditions. This usually introduces ‘noise’ in the picture giving a grainy appearance. Camera Specifications must always be considered with AGC off. |
| ANALOUGE SIGNAL |
|---|
| In Video, the representation of a camera scene by varying voltage in the video signal, the voltage being directly proportional to the light level. |
| APERTURE |
|---|
| The light gathering area of a lens. The iris controls the size of the aperture. |
| ASPECT RATIO |
|---|
| The ratio of the vertical to the horizontal image size. This is 3:4. |
| AUTOMATIC IRIS |
|---|
| A lens that automatically adjusts to allow the correct amount of light to fall on the imaging device. There is a tiny motor and amplifier built in which generally receive a control signal from the camera to maintain a constant one-volt peak to peak (PP) v |
| BACK FOCUS |
|---|
| A mechanical adjustment in a camera that moves the imaging device relative to the lens to compensate for different back focal length of lenses. An important adjustment when a zoom lens is fitted. |
| BANDWIDTH |
|---|
| The amount of space in a given part of the spectrum needed to carry communication signals. |
| BYTE |
|---|
| The basic unit of transmittal and storage for computer data. One byte comprise eight bits. |
| CCD |
|---|
| Charge coupled device, a flat thin wafer that is light sensitive and forms the imaging device of most modern cameras. Nominal sizes can be 1/8”, 1/4”, 1/3”, 1/2”, or 2/3”. There are two types, frame transfer and interline transfer. |
| CD-R |
|---|
| An optical compact disc that can be written to once only. |
| CD-ROM |
|---|
| An optical compact disc that is Read Only Memory. |
| CD-RW |
|---|
| An optical disc that can be written to and over written many times.
|
| C-MOUNT |
|---|
| A C-mount lens can be used on a camera with a CS-mount by adding an adaptor ring to increase this distance to 17.526mm from 12.5 mm. |
| COMPOSITE VIDEO |
|---|
| The complete video signal comprising the sync and video information. |
| COMPRESSION |
|---|
| Methods of reducing the file size of video images. |
| CORE |
|---|
| The central region of an optical fibre through which signal carrying infrared is transmitted. Manufactured from high-density silica glass. |
| CS-MOUNT |
|---|
| A new generation of lenses designed for, 1/2”, 1/3”, 1/4”, and 1/8”, cameras incorporating CS-mount. The distance from the flange surface to the focal point is 12.5 mm. CS-Mounts lenses can not be used on cameras with C-mount configuration. |
| DAT |
|---|
| Digital Audio Tape, a small removable tape cassette used to store computer data. |
| DB |
|---|
| Decibel, a logarithmic ratio between two signals. |
| DEPTH OF FIELD |
|---|
| The proportion of the field of view that is correct focus. The depth of field in focus DECREASE when: the focal length is longer, the F-number is smaller, or the object distance is shorter. |
| DIGITAL SIGNAL |
|---|
| An analogue signal that has been converted to a digital form so that it can be processed by a microprocessor. |
| DSP |
|---|
| Digital Signal Processing, a method of adjusting various parameters of the video signal to obtain improved performance. |
| DVD |
|---|
| Digital Video Disc, a removable disc medium for storing large amounts of image information. |
| DVR |
|---|
| Digital Video Recorder, a method of storing video information in digital form as opposed to analogue recording.
|
| F-STOP |
|---|
| This is the ratio of the focal length to the effective diameter of the lens. (f/A). it is not a measure of the efficiency or the transmission value of the lens. The smaller the f number the more light is passed. |
| FIBRE OPTIC |
|---|
| A very efficient method of transmitting video and telemetry signals over very long distances using fibre optic cable. Signals can be multiplexed and sent alone a single fibre. |
| FIELD OF VIEW |
|---|
| The relationship between the angle of view and the distance of the object from the lens. |
| FIELD |
|---|
| one half of frame consisting of 312 1/2 lines, 50 fields are crated every second. |
| FOCAL LENGTH |
|---|
| The distance between the secondary principal point in the lens and the plane of the imaging device. The longer the focal length, the narrower is the angle of view. |
| FRAME |
|---|
| The Combination of two interlaced fields, 25 frames are created every second. |
| GAMMA CORRECTION |
|---|
| An Electronic correction carried out in the camera circuitry to balance the brightness seen by the camera to that of the monitor. |
| GREY SCALE |
|---|
| The number of shades making up a picture ranging from white to black. |
| HDD |
|---|
| Hard Disc Drive, the magnetic disc used for storing computer data. |
| HERTZ (Hz) |
|---|
| The number of variations or cycles per second. |
| CCTV |
|---|
| Closed Circuit Television simply means that the signals picked up by the cameras are not broadcast over the air, or to a public cable net, but are fed directly to monitors. This may not be fully correct for wireless outfits, but then the range of effective broadcast is minimal, and there is only one intentional receiver.
Camera performance depends largely upon the reflected light at the scene to be surveyed and upon the quality of the imager or sensitive element.
A few fundamental CCTV-surveillance related concepts play an important role when coming to select a CCTV Surveillance system. These terms are listed hereafter:
• Video signal
• Illumination
• Lighting
• Sensitivity
• Resolution
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