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CCTV Video Surveillance Chennai India. About CCTV Video Surveillance Chennai India. CCTV Video Surveillance Products Chennai India. CCTV Related Terms - Glossary Chennai India. CCTV Video Surveilance Sitemap, Chennai India. CCTV Video Surveillance Contact Us, Chennai India.  

F-number (f-stop): Optical or lens speed. Smaller f-number means faster lens.

Focal Length indicates the distance between the optical center of a lens and a video camera's image sensor device. For practical purposes, lens focal length refers to a camera's angle of view. Lenses with a higher focal length number have more narrow, telephoto fields of view. A very low number focal length indicates a very wide field of view. It should also be noted that different cameras (photographic cameras, different imager sizes in video cameras, etc.) will deliver different viewing angles with the same focal length lens.

The distance between the centre of a lens, or its secondary principal point and the imaging sensor. Lower lengths give a greater field of view and less magnification. Longer lengths give a narrower field of view and greater magnification. The table below gives an approximate value for the angle of the field of view for lenses of various focal lengths. 30˚ is considered to be a normal view, telephoto (longer) lenses have lower angles. Most CCTV cameras have one of the 3 sizes of imaging devices listed below, 1/4", 1/3" or 1/2". As you can see, this makes a big impact when choosing lenses.

Focal Length

Imaging Device Size




2.8 mm




4.0 mm




6.0 mm




8.0 mm




12.0 mm




16.0 mm




50.0 mm

Field - Video is generally "phased" (speed of real time display) at a rate of 2 fields per one frame of video. This type of system is referred to as 2:1 interlace. Therefore, fields per second and frames per second do not mean the same thing (this is common misconception in multiple camera processors and DVR recording). The number of fields per second is always twice as high as the number of frames per second. One video frame is composed of two fields; one field consists of the odd numbered lines in the frame and the other field consists of the even numbered lines.

Field of View refers to the angle at which a camera is able to produce a visible image. This angle can be described in terms of diagonal, horizontal, or vertical degrees. A camera's field of view is determined by its lens configuration. Fixed lenses have set fields of view, while cameras with varifocal or power zoom lenses have adjustable fields of view. The width, height or diameter of a scene to be monitored. Usually determined by the focal length of a lens, the sensor format and the distance to the objects.

Fixed Lens - A fixed focus lens has one set focal length with a specific field of view which cannot be changed. Any camera without a varifocal or power zoom has a fixed focus lens. All cameras offered a with fixed lenses are focused to infinity. This means that although the user cannot manipulate the field of view, everything in the picture beyond a few inches will be clear and in focus. Objects simply get smaller as they move further away from the camera (unlike a camcorder which may be focused only on a small area with blurred vision of the video image in the foreground or background of that area).

Fiber-Optic Cable One of the video transmission ways, being used for a long distance transmission up to miles.

Flash Memory Or flash RAM (Random Access Memory). A type of constantly powered non-volatile memory that can be erased and reprogrammed in units of memory called blocks.

Flat Panel Antenna - An antenna for wireless with a flat antenna element contained inside a protective weatherproof housing. As a highly directional antenna, a flat panel is intended to send or receive a propugated radio signal on the same axis as the corresponding antenna on the other end (with line-of-sight visibility between the two whenever possible). While omni-directional antennas are great for short range broadcasts because of their versatility, high gain directional antennas are recommended for most long range wireless video applications.

Frame - a full frame of video is the combination of two image fields interlaced together. A frame is one basic screen capture taken by a camera. 30 frames are displayed in one second of realtime video for NTSC format. PAL format is phased at a rate of 25 frames per second for realtime.

Frames per Second (FPS) describes the number of full video frames displayed or recorded within one second. True real time video consists of 30 frames / sec. for NTSC format and 25 frames / sec. for PAL format. Be sure not to confuse frames per second with "fields per second" or "images per second". A complete frame of video is compiled of two separate images (or fields), so the number of fields in one second is always twice the number of frames per second.

FPS Display Rate (a.k.a. screen refresh rate) indicates the number of frames per second a VCR or DVR recorder will display on a monitor for simultaneous viewing. Please DO NOT CONFUSE this specification with FPS Record / Playback Rate. The rate at which each camera is displayed is often NOT the same as the number of frames per second the recorder captures for playback. Many DVR sellers flash "real-time display rate" or "30 frames / sec. display rate" but do not in fact offer realtime playback of recorded video.

FPS Record Rate describes exactly how many frames per second a video recorder can actually capture. Analog recorders like VCRs can easily record in realtime (30 frames / sec. for standard NTSC) or timelapse (fewer than 30 frames / sec. for NTSC). Many digital DVR recorders, however, cannot record actual realtime video. Many sellers try to mislead consumers by advertising FPS Display Rate instead of actual record rate. For most situations, recording rate is the spec to pay attention to. However, please note specifications for digital video equipment are not the only numbers to rely on. In fact, many DVR recorders outperform their specifications upon real world testing while other low quality units often record at a much slower rate than their specs claim.

Frequency is the number of competed cycles of an electronic signal that occur in a given length of time. Frequency is usually measured in cycles per second (Hertz, Hz). For most CCTV industry equipment, frequency is used to describe the RF radio frequency at which wireless equipment operates. Frequency can also be used to describe the cycles of electrical current for the signal system.

FTP File Transfer Protocol a way to exchange files between computers on the Internet.