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F-number

F-number describes how bright a lens is.  In other words, it represents the maximum amount of light that a lens can direct to the camera’s image sensor.   This amount of light is determined by the widest iris opening that the lens allows or its maximum aperture and the focal length of the lens. F-number is described as a function of the focal length (f) of a lens and the maximum diameter (D) of the iris opening as follows: F-number = f (focal length)/D (maximum iris opening).  A lens with a smaller F-number provides brighter images.

Fiber Optics

Light transmission through optical fibers for communication and signaling.  It is a technology that transmits information as light pulses along a glass or plastic fiber.  Optical fiber carries much more information than conventional copper wire and is generally not subject to interference.  Most telephone company long-distance lines are optical fiber.

Fickerless

Cognizant, constant, reliable, resolute, stable, steady, unchanging.

File Transfer Protocol (FTP)

It is a standard widely used over a TCP computer network, such as the internet, to exchange and manipulate files between two computers on the Internet.  An FTP client may connect to an FTP server to manipulate files on that server.

Filter

A coloured piece of glass or other transparent material used over the lens to emphasize, eliminate, or change the color or density (ND) of the entire scene or certain areas within a scene.  Also see "colour temperature".  Technically, it explained as a piece of material which restricts the transmission of radiation.  Generally it is coloured to absorb light of certain colours.  It can be used over light sources or over the camera lens.  Camera lens filters are usually glass either dyed or sandwiching a piece of gelatin in a screw-in filter holder.

Firewall

A firewall works as a barrier between networks, e.g. between a Local Area Network and the Internet.  The firewall ensures that only authorized users are allowed to access the one network from the other.  A firewall can be software running on a computer, or it can be a standalone hardware device. 

Fixed Focus

Describes a non-adjustable camera lens, set for a fixed subject distance.

Fixed Focus Lens

A lens that has been focused in a fixed position by the manufacturer.  The user does not have to adjust the focus of this lens, applies on most entry cameras.

Focal length

The focal length is defined as a distance from the center of such a convex element (principle point) to the focal point (image plane) and it is one of the most decisive factors that determine the characteristics of a lens.  The focal length of the lens on most adjustable cameras is marked in millimetres on the lens mount.  It is the distance from the principal point to the focal point.  With CCTV camera lenses, the focal lengths usually start at around 2 to 4mm, and up to 50mm and so on.  Lenses do come in discrete values, so you cannot order a particular size lens, ie: 6.25mm.  Common focal lengths are: 2.8mm, 3.5mm, 4mm, 8mm, 12mm, 16mm, 25mm, 50mm, 75mm.  Lenses shorter in focal length (eg 4mm) give a wider angle of view and are called wide angle lenses.  Lenses with longer focal length (eg 16mm) are called "telephoto", narrow the view and therefore they look as if they are bringing distant objects closer.

Focus Range

It refers to the range within which a camera is able to focus on the selected picture subject, 4 feet to infinity, for example.

Focus Tracking

This enables the camera to analyze the speed of the moving subject according to the focus data detected, and to obtain correct focus by anticipating the subject's position and driving the lens to that position and at the exact moment of exposure.

Frames per second (fps)

Digital video cameras come in two different image capture formats: interlaced and progressive scan. Progressive or noninterlaced scanning is a method for displaying, storing or transmitting moving images in which all the lines of each frame are drawn in sequence. This is in contrast to the interlacing used in traditional television systems where only the odd lines, then the even lines of each frame (each image now called a field) are drawn alternately.  50 interlaced fields = 25 frames is the standard video field rate per second for PAL television.  Format used in Europe has a frame rate of 25 frames per second for motion pictures to create a smooth moving image.

Full-duplex

It means transmission of data in two directions simultaneously.  In an audio system this would describe e.g. a telephone system.  Half-duplex also provides bi-directional communication, but only in one direction at a time, as in a walkie-talkie system.