F-stop:
is the ratio between the focal
length of the lens and the effective diameter
of the iris opening. It indicates the light
gathering ability of the lens. 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:
is the distance between the optical
centre of a lens and the point of focus.
It is usually measured in mm or inches.
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). |
