Housings for large lenses.
Although the housing is not a high-tech product, it is impossible to use the most advanced control and positioning systems for a television surveillance camera without it. The largest part of such cameras is the lens.
The factors that determine the size of the lens are basically two: the focal length of the lens “f” and the aperture ratio “F”. The focal length is directly proportional to the size of the lens, while the F-number is inversely proportional to the size of the lens. Therefore, large lenses with large focal lengths “f” can be quite compact due to the low aperture ratio F. Accordingly, for such a lens paired with a standard CCTV camera, a standard thermal housing will be sufficient.
The numbers “f” and “F” also determine the cost of the selected lens. Moreover, the price of standard models of motorized ZOOM lenses varies from 0 to 0, while the cost of the most advanced models exceeds 000 per piece.
Unlike installing a camera in a conventional thermal housing, a housing for large lenses implies the use of a television surveillance camera in specific conditions, namely:
installation on a pan-tilt platform, since it is impractical to use a large ZOOM lens directed at one point, without the ability to control the rotation/tilt of the television camera;
outdoor installation. In most cases, a standard rotating high-speed dome camera is sufficient for indoor use, while outdoors at distances of more than 50–100 m, specialized lenses with focal lengths that are inaccessible for high-speed “domes” come to the rescue;
increased requirements for the temperature conditions inside the casing, since the lens has many mechanical moving parts that will simply freeze and stop moving at significantly negative temperatures, and at high temperatures they can be subject to thermal overloads.
Under these conditions, the casing for such a camera must provide the following characteristics:
have a large internal volume that corresponds to all devices that can be installed inside the casing: lens, camera, heating element with thermostat, camera power source, transmitting device;
a special distributed heating/cooling system for the internal volume of the casing to ensure uninterrupted operation of the mechanical parts of the ZOOM lens;
a windshield wiper system must be installed optionally;
the casing must be mechanically strong, since the weight of the lens often exceeds 2-3 kg, and when turning/tilting the camera, significant dynamic loads occur, which can lead to inaccurate positioning of the camera and ultimately cause a malfunction of the PTZ camera;
the casing should not significantly exceed the dimensions of the contents of the casing, since in this case wind loads will increase, which will be reflected in the image in the form of picture shaking at significant focal lengths.
A number of manufacturers have models in their lineup designed for installation of cameras with large lenses, several models are presented in this review.
Linea 3 Tekno System (Italy)
The Linea 3 casing has an aluminum casting design for strong fixation and a large internal volume. The consumer can choose from two casing lengths — 400 or 500 mm.
The housing has a side opening for easy access to the camera and lens and a side connection, which simplifies installation. There is also a heater with a thermostat, a fan kit for use in hot climates. Options that are not included in the basic package, but are in constant demand, are vandal-proof and anti-fog (double-glazed) glass.
Adapter plates provide mounting of the housing on various pan-tilt platforms.
CHEG Protective Housing (CBC Group)
The CHEG protective housing is sold under the Computar trademark. The housing has an IP66 protection class and is designed to work with large-size zoom lenses. The operating temperature range of the CHEG housing is from -40 °C (provided that a double heater is installed) to +50 °C.
The external dimensions of the housing: 154 x 156 x 439 mm and a viewing glass with dimensions of 94 x 80 mm allow this housing to be used with almost all the largest television cameras and zoom lenses from various manufacturers.
The impressive internal dimensions of the housing with a cross-section of 134 x 88 mm allow you to place in it not only a TV camera, but also the largest lenses produced by Computar: 27x zoom lens H27Z1970AMS with a focal length of 19 to 513 mm or 34x zoom lens T34Z series with a focal length of 5.5 to 187 mm.
CHEG has a highly durable housing construction made of pressed aluminum. A special paint coating will preserve the appearance of the housing for many years of its use.
Thermal housing HGV (VIDEOTEC)
The thermal housing HGV allows you to protect cameras with the largest zoom lenses available on the global video surveillance market.
HGV has a special reinforced mechanical structure made of aluminum and a built-in sun visor made of impact-resistant ABS polymer material. A special glass cleaner is integrated into the housing, located so that it does not fall into the camera's field of view. The housing is equipped with 3 heating elements and a built-in fan. To facilitate the installation and configuration of the camera, the upper part of the housing can be completely removed.
The new HGV housing is used when installing the camera in difficult outdoor environments such as open area fire monitoring, public safety, marinas, coastlines, airports and open spaces. The usable internal dimensions are 156 x 139 x 519 mm.