F-stop:
The lens usually has two measurements of F stop or aperture, the maximum aperture (minimum F stop) when the lens is fully open, and the minimum aperture (maximum F stop) just before the lens completely closes. The F stop has a number of effects upon the final image. A low minimum F stop will mean the lens can pass more light in dark conditions, allowing the camera to produce a better image at night. A maximum F stop may be necessary where there is a very high level of light or reflection, as this will prevent the camera from "whiting out", and help maintain a constant video level. All auto iris lenses are supplied with Neutral Density spot filters to increase the maximum F stop. The F stop also directly affects the depth of field.

Fast lens:
is a lens which can gather and transmit more light to the camera. A fast lens has a larger iris opening and therefore a smaller F-stop.

Fast scan video:
is a method of sending video images over the telephone network to any part of the world. The update rate presently is not real-time but is improving continuously.

Fence disturbance sensor:
is a type of sensor installed around the perimeter fence in a site to detect any intrusion. There are many types of fence disturbance sensors available. In CCTV it can be interfaced with a switcher. to switch a nominated camera for extended viewing.

Fibre optics:
is a method of modulating video, audio or data with a light beam and transmitting it along a glass core.

Field:
is one half of a frame and consists of 312.5 (PAL) and 262.5 (NTSC) lines. Odd and even fields are combined to form a single frame.

Field of view:
is the height and width of the view that can be seen through a lens.

Fixed lens:
is a lens with a fixed focal length. A wide range of fixed lens are available to suit different applications e.g. 2.6mm, 4.8mm, 8mm, 16mm, 25mm, 75mm etc.

Flexi conduit:
is a flexible PVC conduit which is used at the camera point to enclose loose cables between the camera and the junction box or wall.

Fluorescent lamp:
is a type of artificial light source in which the mercury vapour generated by a low wattage arc strikes the phosphor material to emit light. It is popularly used in indoor applications.

Fly back period:
is the time taken to move from the end of a field, frame or line to the start of the next field, frame or line. It is also called the retrace period.

Focal length:
The focal length of the lens is measured in mm and directly relates to the angle of view that will be achieved. Short focal lengths provide wide angles of view and long focal lengths become telephoto, with narrow angles of view. A "normal" angle of view is similar to what we see with our own eye, and has a relative focal length equal to the pick up device. Our online lens calculator is a simple to use device for estimating focal length, object dimension, and angles of view.

Focus ring:
is a ring on a lens which is rotated to obtain correct focus. It is available only in manual iris lenses.

Foot candle:
is a unit of illuminance. 1 foot candle = 1 lumen of light incident on 1 sq. ft of surface area.

Frame interline chip:
is a type of CCD chip which is expensive to manufacture and is currently used in broadcasting video cameras. It overcomes many shortcomings of the existing CCD chips used in CCTV cameras.

Frame switching:
is a process used in multiplexers or multirecorders in which a frame is picked up from each camera in turn.

Frame store:
is an electronic device used to capture and digitally store a video image. It can be an independent unit or in built in other equipment like fast scan video transmitters or video motion detectors.

Frame transfer chip:
is a type of CCD chip in which the pixels have a dual role of sensing the light and transferring the charge. This causes picture smearing, a major shortcoming of this chip.

Frame:
is the basic unit of a moving picture. A frame contains 625 lines (PAL) or 525 lines (NTSC).