Measure twice, cut once. That’s the saying we’ve all heard from professional builders and carpenters. However, this saying extends to more than just sawing wood or hammering nails. For cameras installed with a fixed focal length lens, measuring for field of view must be precise. To use another phrase, once the camera is fixed in place, what you see is what you get. Considering the many video surveillance cameras available, a camera with an adjustable lens will give you greater flexibility during installation and keep you from timely labor spent on relocating cameras if your needs change in the future.
While some security surveillance cameras may be pre-packed with a lens, like dome cameras (hyperlink dome cameras), not all lenses are alike. There are three main categories of lenses: fixed focal length with a manual iris, vari-focal length with a manual iris, and vari-focal length with an automatic iris. The automatic and manual iris label describes how much light the lens will allow the camera to see as the lighting conditions in the environment changes. If lighting will remain constant, like in an office setting, a manual iris is a great option because you will only need to adjust the iris during installation. But, if light in the environment changes over the course of the day, an automatic iris is your best choice. To illustrate the difference, imagine going to the optometrist for an eye exam. When the optometrist dilates your pupils it is the equivalent of seeing with a manual iris. Your pupil, like the iris of a camera lens, is forced to allow as much light as possible. In a dim room, you see clearly but when you walk outside your eyes are flooded with light which makes your vision out of focus and creates blind spots within your field of view.
The fixed length or vari-focal length refers to the ability to adjust the camera’s field of view. Vari-focal lenses are typically found in a 2.8mm to 12mm, 4mm to 9mm, or 5mm to 50mm configurations. Fixed focal lenses are available in in various sizes but are limited in scope (fixed) to the noted lens size. The smaller the lens size, the wider the field of view. Depending on the distance between the installed cameras and the point of interest, camera lenses with the same focal length will produce different fields of view. Therefore, before you make a camera selection, know how you want the camera to perform.
Security surveillance cameras generally have three uses: to survey an area for disturbance, monitor behavior, or identify individuals. If your goal is to survey an area such as a parking lot, select a lens with the widest field of view. To monitor behavior, such as making sure a grocery store clerk stays at their register during their shift, a mid-range lens is ideal. However, if you want to have enough detail to help police identify someone you don’t know, like a robber entering a convenience store, a longer range lens is needed. If you are unsure how your camera will be used, if your use will change over time, or you would prefer to have some flexibility in your installation height and field of view, choose a camera and lens combination with a vari-focal length and automatic iris lens.