#covert video surveillance
Covert video surveillance.
( Attention! This is an introductory article; you cannot order covert video surveillance on the site.)
Openly used video surveillance helps combat crime in all its manifestations.
Covert surveillance, in theory, should not give offenders any indication that their actions are being watched.
Video recording can also be made, which can then be used to bring charges against the offender, justify him or punish him.
Open video surveillance systems are good for finding offenders, but in some cases, investigative bodies, police and government officials, retail operators and security firms require the use of hidden cameras.
Covert and overt video surveillance are often used together to catch professional criminals.
A criminal, having discovered an overt video system, tries to destroy or disable the cameras, but all his actions are recorded by hidden cameras.
In some cases, the reason for installing covert video surveillance may be the desire to preserve the architectural aesthetics of a building or the area adjacent to it.
Hidden video surveillance cameras and lenses have become widespread, and despite the fact that the optics used in them are very small, this type of equipment can provide very high-quality video images.
Hidden cameras are usually disguised as “ordinary” objects or placed behind small holes in opaque surfaces (such as walls or ceilings).
To camouflage cameras, ordinary objects are used — lamps and light fixtures, tables and wall clocks, radios, books. A very effective covert video surveillance system uses a camera and lens disguised as a sprinkler head of a fire extinguishing system located on the ceiling.
In this chapter, we will analyze the principles and technologies of covert video surveillance, as well as unique point lenses and cameras.
The lenses that will be discussed have a small diameter of the front lens, which allows the lens and camera to provide a view of the observed scene through an opening with a diameter of 1/16 inch.
Most of these lenses have a medium and wide viewing angle — from 12° to 78°, which allows them to capture images from relatively large spaces, while providing the ability to both identify people in the frame and observe processes and events occurring in the control zone.
Below we also consider special versions of spot lenses: angular, with automatic diaphragm, built-in sprinkler and fiber optic; information is also provided on miniature spot cameras, which consist of a lens and matrix, combined into an ultra-small camera head, as well as on some other miniature cameras.
In applications that require observation in conditions of low illumination of the object being photographed, cameras based on highly sensitive CCD matrices are used, and an infrared light source is used to increase the contrast of the image.
Since many of the covert video surveillance systems are deployed temporarily at sites, wireless data transmission is used to transmit video signals from cameras to monitors, recording devices, or video printers.
Technical principles of covert surveillance.
Hiding lenses and cameras from prying eyes is accomplished by placing the lens behind one small-diameter hole, multiple small-diameter holes, or on the other side of a translucent mirror.
The options for installing hidden cameras include placement in ceilings, walls, lamps, clocks and other objects that do not arouse suspicion by their presence in the room.
Depending on the expected activity in the surveillance zone, one or more cameras are installed. Due to the use of small-sized optics in hidden systems, they are characterized by specific problems that are not present in open-type systems, where the lenses have standard sizes.
Since the placement conditions require that the diameter of the front lens be as small as possible, the hidden lens must have a minimum F-number, collecting and transmitting the maximum possible amount of light from the object to the light-sensitive element of the camera. To meet these requirements, so-called pinhole lenses are used in covert systems.
The term «pinhole» — literally translated as «the size of a pinprick» — does not quite accurately characterize the size of the lenses, since the range of diameters of their front lenses is 1/16 — 3/8 inches.