One of the main considerations when installing a security surveillance system is the lens. Without lenses, the system would be useless. Most cameras come with a choice of lenses, while box type security cameras require you to choose the lens and purchase it separately.
When choosing a lens, there are a few things to keep in mind. First, how far do you want to see, and what level of detail do you want to see. Lenses with a fixed focal length are simply known as fixed lenses. Fixed lenses are available in a variety of focal lengths, however, the most common fixed lens is a 3.6mm lens. This lens will give you approximately 75 degree field of view and will allow you to see a fair amount of facial detail up to about 30 feet. This would be a great choice for an overview camera.
If an overview camera is not sufficient to capture the desired field of view or distance, then lenses with various focal lengths can be used to achieve the desired result. The human eye equivalent of a CCTV Lens is a 3mm lens. So, anything smaller than that would be considered a wide angle lens and anything larger would be considered to have some level of magnification. For example, a 2mm lens would allow you to capture a much wider angle of view than the human eye, but the distance that you could see in any detail would be small. In comparison a 100mm lens would allow you to see a high level of detail at a great distance, but the angle of view would be very narrow.
Let’s suppose that you aren’t sure what distances or angle of views will meet your needs, or that the distances and angles may change from time to time. Then, in that case, a lens with a variable focal length would be needed. These types of lenses are known as varifocal lenses. These lenses are basically manually operated zoom lenses. Varifocal lenses are also available in a variety of focal length ranges. One of the most common sizes of varifocal lens is a 2.8-12mm focal length. This lens can be adjusted from 2.8mm (wide angle) to 12mm (zoom) to accommodate a range of camera requirements.
Although varifocal lenses would be considered zoom lenses, in the security industry a zoom lens is a lens that can be mechanically or electrically zoomed. These types of lenses can be remotely zoomed in or out from the DVR or other remote method. This would allow the camera to act as an overview camera most of the time and then be zoomed to capture a small detail when needed. The most common zoom lens you will find is a part of a Pan/Tilt/Zoom or PTZ type of camera. These lenses have a motorized zoom, while the camera itself has a motor allows the camera to move up or down and rotate.
The camera lens is like the human eye; without them we couldn’t see. Without lenses, your security surveillance system would not be able to capture images. And, just as we use telescopes and magnifying glasses to enhance our vision, you can enhance the functionality of your surveillance system to maximize its capabilities.