Getting the most out of your dome

It is no wonder dome cameras are so popular – they are robust, unobtrusive, can see in bright or low light and most importantly conceal the direction the lens is pointing. Milind Borkar looks what other features you should specify from your security systems installer

Dome cameras are typically used in locations where you do not want people to know the direction the camera is pointing and for cameras with a PTZ capability a dome housing will enable the camera to have an unobstructed view no matter where it is looking. PTZ dome cameras can cover a wide area by enabling greater flexibility in pan, tilt and zoom functions. They enable a 360-degree, continuous pan and a tilt of usually 180 degrees.

Some end-users see value in a dome housing even when using a fixed camera for wall-mount or ceiling-mount applications, because the dome can provide a more pleasing appearance. For example, fixed mini-dome cameras, measuring only a handful inches in diameter, are perfect for installations where appearance is a chief consideration.

Selecting a PTZ dome

First of all look at how quickly your PTZ camera changes positions is a major consideration. For example, a camera may move up to 280 degrees per second when moving into a pre-set position but only 100 degrees per second when security personnel control the device manually. Speed domes, which quickly move through a series of positions, provide an alternative, especially if there are many points to monitor with a single camera or if the threat is fast moving.

Another important factor when selecting PTZ cameras is the number of pre-set positions that can be pre-programmed into the camera. Pre-sets are a series of positions that a camera can be programmed to automatically go through during the course of a tour, shift or day to help ensure that a specific area is covered or when a video surveillance system is integrated with an alarm or access control system. The camera can be programmed to go to an appropriate pre-set position when a certain event occurs, for example, when a door is opened.

In preset mode, positioning accuracy from one view to another is critical. Poor positioning accuracy results in a camera not pointing to the scene an operator selected for a stop on the tour. In regard to forensics, this can create useless evidence when suspicious activity needs to be reviewed. Look for cameras with a preset accuracy of 0.1 degrees.

A PTZ dome camera can also provide a guard tour mode, whereby the camera automatically moves from one preset position to the next in a pre-determined order or at random. Normally up to 20 guard tours can be set up and activated during different times of the day. In guard tour mode, one PTZ dome network camera can cover an area where 10 fixed network cameras would be needed. The main drawback is that only one location can be monitored at any given time, leaving the other nine positions unmonitored.

Privacy masking

3D privacy masking is supported in most PTZ dome cameras and lets selected areas of a scene be blocked or masked from viewing and recording. Masking is maintained even as the camera’s field of view changes through panning, tilting and zooming as the masking moves with the camera’s coordinate system.

In outdoor installations, PTZ dome cameras with zoom factors above 20x are sensitive to vibrations and motion caused by traffic or wind. Electronic image stabilisation (EIS) helps reduce the affects of vibration in a video. In addition to getting more useful video, EIS will reduce the file size of the compressed image, thereby saving valuable storage space.

When a PTZ dome camera is mounted on a ceiling and used to follow a person, there will be situations when a person will pass just under the camera. When following through on the person, images would be seen upside down without an E-flip functionality, which electronically rotates images 180 degrees. It is performed automatically and will not be noticed by an operator.

One of the limitations of a fixed dome camera is that the choice of lenses is limited by the space inside the dome housing. To compensate for this, a varifocal lens is often provided to let the camera’s field of view be adjusted.

Vandal-proof domes

Whether PTZ or fixed domed cameras are part of a legacy installation or when buying new gear, security executives need to consider the environment in which the camera will work. Some cameras have vandalresistant and ruggedised domes, which can be important when a camera is mounted in an area that could be reached with a baseball bat or weapon.

Other cameras may require a separate housing for vandal protection. Special housings also may be needed if a camera will be installed outside. In certain climates, there is need for a heater and, for certain areas, need of a hidden blower. Sunshields also can play an essential role for some outdoor applications. Depending on an end-user’s type of business or industry, housings that protect from water damage or dust are available as are housings with a pressurised seal.

pressurised dome cameras feature a nitrogen pressurised environment inside the housing with a stainless steel rim for maximum protection against airborne contaminants and moisture. Special valves minimise decrease in pressure over time. Solid-state sensors in the housing relay important system information, such as internal temperature and pressure readings, back to the control centre. Non-volatile memory in the housing enables automatic downloads of camera presets and other data in the event that the camera and drive module must be replaced. There are also night vision dome cameras that will see in total darkness and can be vandal proof as well as used indoor and outdoor.

Milind Borkar is Infinova vice president - Middle East, India and Africa. For more information visit: www.infinova.com