Hidden video surveillance
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Openly used video surveillance helps combat crime in all its manifestations. Hidden surveillance, in theory, should not give violators any signs that their actions are monitored. At the same time, video recording can be made, which can later be used to bring claims against the violator, justify him or punish him. Open video surveillance systems are good at helping to find violators, however, in some cases, investigative authorities, police officials and government agencies, Retail operators and security companies also require the use of hidden cameras.Covert and overt video surveillance are often used together to catch professional criminals. The criminal, having discovered an open video system, seeks to destroy or disable the cameras, but all his actions are recorded by hidden cameras. The reason for installing hidden video surveillance in some cases may be the desire to preserve the architectural aesthetics of the building or the area adjacent to it.
Cameras and lenses for covert video surveillance have become widespread, and despite the fact that the optics used in them are very small in size, this type of technology can provide very high quality video images. Hidden cameras are usually disguised as “regular” objects or placed behind small holes in opaque surfaces (such as walls or ceilings). To camouflage cameras, common objects are used — lamps and lamps, 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 spot lenses and cameras. The lenses in question have a small front lens diameter, which allows the lens and camera to provide a view of the scene through a 1/16-inch diameter aperture. 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 making it possible to both identify people falling in the frame and monitor processes and events occurring in the control area . Below we consider special versions of point lenses: angular, with automatic diaphragm, built into a sprinkler and fiber optic; Information is also provided on miniature point cameras, which consist of a lens and a matrix combined into an ultra-small camera head, as well as some other miniature cameras.
Applications that require low-light surveillance of the subject use high-sensitivity CCD cameras and an infrared light source to enhance image contrast. Since many CCTV systems are deployed temporarily on sites, wireless data transmission is used to transmit video signals from cameras to monitors, recorders or video printers.
Technical principles of covert surveillance
Hiding lenses and cameras from prying eyes is carried out by placing the lens behind one small hole diameter, many small diameter holes, or on the other side of a translucent mirror.
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 area, 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 absent in open-type systems, where lenses have standard sizes. Since placement requires 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 subject to the photosensitive element of the camera. To meet these requirements, hidden systems use so-called pinhole lenses. (The term pinhole — literally translated as «the size of a pinhole» — does not accurately describe the size of the lenses, since the diameter range of their front lenses is 1/16 … 3/8 inches. )
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