SELECTION OF CAMERAS
Before going into technical details, we must answer the question where we would like to install our cameras and what they are supposed to monitor. I will explain it in more detail in the following sections. But already at the beginning, we have to ask ourselves the following questions: Will the cameras be installed indoors or outdoors? Should they keep looking at the same place or you want to move them? What area should be visible on a recorded film? The priority is what you want to achieve, and to achieve that you should choose cameras (whether IP or AHD devices) with specific parameters. Once you read the following sections, you will certainly know which IP or AHD camera you should buy to meet your expectations.
The matrix is the component responsible for recording the image falling on it through the lens. It consists of many light-sensitive elements, which enable the conversion of light into electrical pulses. The basic parameter of each matrix is its resolution. It is the resolution of camera matrix that determines the maximum resolution of the image recorded. In the case of IP cameras, resolution is expressed in MP (megapixels), while in the case of AHD cameras it is given in points (lines) in vertical line. It also happens that the manufacturers of AHD cameras give the resolution in MP, like for the IP cameras. The present typical resolutions of IP cameras are: 1MP, 2MP and 5MP. The AHD system is dominated by 1080p cameras, which corresponds to 2MP. Let me remind you that 1080p is the so-called Full HD, that is the resolution used by most TVs in our homes. This means that such a TV allows you to fully use the image generated by such a camera. When it comes to 4K televisions, you can view an image from four cameras without losing its quality. If you connect your Full HD television to a camera with a higher resolution (e.g. 5MP), you will not be able to fully appreciate the image quality, as the camera will provide a higher resolution that the TV! Similarly, if you try to view an image from four cameras on a Full HD television, the image from each camera will be scaled down.
- Lens focal length – the angle of view in IP and AHD cameras
Focal length of the lens is a parameter that translates into the angle of view of the camera in which it is installed. Unfortunately, it is impossible to directly translate the focal length into the angle of view, as it also depends on the physical diagonal used in the camera matrix. The same lens installed in a camera with a 1/3” or 1/4” matrix will give a different angle of view. Therefore, when choosing the camera you should pay attention to the width of the angle of view, not the lens focal length.
Well, but what is the angle of view and why is it important?
The camera’s angle of view determines the width of the video image recorded by the camera. If you direct your camera on, say, an entrance gate, you often want to have a maximally accurate image of the vehicles passing it (including their licence plates), and you completely don’t care about recording the surroundings of the gate. If you properly choose the angle of view, you will get more pixels showing the elements of your interest, which in practice means a better image. On the contrary, if the angle of view is too wide, a part of the image will be taken by unnecessary elements, and the image of the gate will be less accurate. In yet another case, if the angle is too narrow, a part of the image of your interest will be beyond the area covered by the camera.Where it is necessary to precisely adjust the angle of view, we use cameras with a variable lens. The adjustment is made by a relevant knob or screw installed in the camera housing. If a precise adjustment is not required, we use cameras with an adequate fixed lens.
- Pan, Tilt, Zoom (PTZ) features in IP cameras
In most surveillance systems, we use cameras with a fixed angle and lens, or with a lens adjustable on installation. They are sufficient to monitor the surroundings but do not enable active surveillance (tracing a moving object or zooming in the image so that the object of interest is visible as well as possible). If this is required, the necessary help is provided by PT or PTZ cameras. The acronym stands for: Pan – panoramic motion, that is the rotation around the camera’s own axis; Tilt – the ability of the camera to tilt; and Zoom – changing the focal length (zooming in).
<Rysunek kamery PTZ>
The features generally apply to the IP cameras but may also be provided by some AHD solutions. PTZ cameras make it possible to manually control the camera motion and provide the so-called patrol option (that is when the camera passes a pre-set path). In advanced systems, the PTZ cameras can work with fixed cameras, serving as a kind of “searchlight” which picks up suspicious objects (e.g. at airports).
- Types of camera housings
The IP and AHD cameras can be installed in many different housings. This makes it possible to choose a camera suitable for a specific place of installation, taking into account and ambient conditions and damage resistance.
Bullet – a camera mounted at the wall or ceiling, with a remote position control. Low resistance to vandalism.
Dome – a camera mounted mainly at the ceiling, its position can be adjusted after removing the housing. Higher resistance to the acts of vandalism, especially in the versions with an increased impact resistance (IK rating).
PTZ (dome) – usually has the form of a fixed base and rotary head, which can also move up and down. No resistance to the acts of vandalism, and usually no resistance to environmental conditions.
External PTZ housing or so-called chandelier (but to be precise, it should be called a wall lamp) – a specialised housing type, where the head with the lens is protected by a glass dome, similarly to the typical dome housings. It is highly resistant to environmental conditions and resistant to the acts of vandalism according to the assigned IK rating.
The above types of housing are the most popular solutions, but of course these are not all available variants.In their descriptions, I have mentioned the resistance to environmental conditions. Its classification is standardised and specified by a parameter called IP rating (International Protection Rating). Camera specifications express this rating as an IPxy value, where x stands for resistance to solids (including dusts) and y stands for resistance to liquids. Cameras operating in dusty environments or outdoors must have an appropriate protection rating.
- Night vision – lighting
Most light-sensitive matrices used in cameras have a specified minimum level of ambient light which is sufficient for proper video recording. As the ambient light weakens, the image gets degraded until a point where it is completely unclear. To avoid a situation where one cannot record a video image at night, they have developed a system composed of IR light diodes and the IR Cut filter. When the light level drops to a pre-set threshold, the camera activates its lighting system, opens the filter and switches to the night mode. With this, we can record a clear image even when there is insufficient ambient light. In consequence of using IR diodes, we get a monochromatic image in the shades of grey. The issue was solved by Sony. Recently they made available new solutions, which enable image recording at a very low light level, which makes it possible to record a colour image even after sunset. The marketing name of the solution is Starvis, and the cameras with these matrices should be chosen where it is necessary to record a colour image at a weak light.