Mostly all security cameras used nowadays have an integrated, matched lens, yet integrated-lens cameras still require interpretation of conditions specific to the security application, as well as an understanding of the camera’s capabilities.
The horizontal Field of View (FOV) is dictated by the distance of the lens from the image sensor, therefore before deciding how many megapixels you need, you must consider what the FOV should be and once you’ve determined where to install the camera and figured out what the FOV is, you should consider the resolution which you require, based on the distance from the subjects.
Ambient Light Levels
Ambient light levels are another important element of the security environment as it is crucial to install a camera which produces clear images during operational hours. The amount of ambient light present dictates how much light sensitivity your surveillance system requires. The amount of light able to pass through a lens is indicated by the f-stop number, which means that the smaller the f-stop, the more light that can pass through the lens.
Fixed, Vari-focal and Autofocus
Vari-focal or zoom lenses provide a convenient way to improve the field of view during or after installation. Motorised vari-focal lens can be adjusted from a computer and would result in a better ROI for the end-user if an application requires frequent lens adjustments. Manual vari-focal lens must be adjusted during installation and require you to physically focus the lens, while fixed lenses have a fixed focal length and cannot be adjusted, which generally cost less than vari-focal lenses. It is possible to reduce focus issues significantly by choosing a camera with an autofocus feature, which would eliminate the problem of focus shift as day turns to night. However, if you’re using a wide-angle lens, there’s usually less need for autofocus, as a lot of the FOV is going to be in focus already.
The wider the FOV, the better the situational awareness, however there is no wider FOV than 360 degrees. Fisheye cameras can provide up to a 360-degree hemispheric view, which lets you see in all possible directions. It is important to consider that fisheye cameras produce considerable optical distortion, therefore images are best viewed in playback or dewarp. It is most beneficial to use a recorder which has local dewarping, as if you avoid in-camera dewarping, everything that the camera captures would be recorded for later viewing. While in-camera dewarping means that the camera would be compatible with just about any recorder.
How successful video surveillance systems are depends on the factors which are identified and addressed during its specification and installation. The coverage area, level of image detail which is required and ambient light all help guide the lens selection.