A security camera is only as good as its lens; if you've ever tried to take a picture with the lens cap on, you know what I mean. Likewise, the wrong type of lens, or one that's low-quality, can negatively impact your security camera's performance.
If you've invested in a CCTV system, you want the best possible results: a clear picture of the area you're monitoring, with all the necessary details. The camera's lens determines how much area the camera covers, how clearly you can see details (especially in the distance), and how much light enters the camera. Here are a few things to consider when buying a CCTV camera lens.
Focal Length CCTV Camera Lenses
The focal length of a lens determines how far the camera can see, and is either fixed or variable. Fixed focal length means the focal length can't change, so you have to position the camera the correct distance from your target area. These lenses are less expensive than vari-focal lenses, which you can adjust manually, and zoom lenses, which you adjust electronically. Adjustable focal lengths are good for when you have a moving target, or if you need to see details in different parts of the scene.
CCTV Lense Views
The field of view determines how wide an area you can see. The bigger the focal length, the narrower the field of view-that is, the more you zoom, the less area you see, and vice versa. Keep in mind that it's hard to make out details in a wide field of view. A 2.5-4 mm focal length, for instance, gives you a wide field of view-about 75 to 180 degrees (i.e., fisheye)-but details are often distorted.
This is fine if you want a panoramic or broad view of the scene, but if you want to see specific details at a distance (i.e., facial features or nametags) or zone in on a particular spot (i.e., an approaching figure or a doorway), you're better off with an 8 or 12 mm focal length.
The Iris of CCTV Lenses
The lens iris determines how much light enters the camera. A fixed iris lens is best for conditions where the lighting is good and doesn't change (i.e., electrical lighting, usually indoors). If the lighting is extreme (very bright or very dim) or only changes occasionally, the manually adjustable manual iris lens is worth your while-mainly because it's cheaper than an auto-iris lens, which automatically adjusts to changing lighting conditions and is best for outdoor surveillance.
Specialty Camera Lenses
There are lots of lenses out there. Besides your run-of-the-mill camera lens, you can get lenses with a variety of special features that can come in handy for surveillance purposes.
- Telecentric lenses, for instance, actually readjust the light beams entering the camera so that the focus stays the same no matter how far away the camera is; that is, there's no distortion of the image at any distance, so you can see all the details of an object accurately. That means you can correctly measure distances and dimensions-convenient if you need to know, for instance, the perpetrator's true height or the size of their car.
- Large format lenses are designed for megapixel cameras with large digital sensors. These lenses minimize distortion, have enhanced contrast and depth-of-field, and are excellent for close-ups.
- In the zoom lens family, you have auto-focus zoom lenses that automatically adjust the focus when the object or camera shifts position-again, useful for moving targets. You won't, for example, lose the details of a person's face just because they're walking around or running off.
- You can also get high-magnification zoom lenses, which, as one might guess, have a higher zoom range and are good for viewing objects at extreme distances. These are available on their own or as accessory components for other zoom lenses.
- An auto-focus and high-magnification zoom lens combination can literally go a long way. Remember, your choice of lens makes a big difference in the images your security camera picks up. Assess your security needs, your CCTV system capabilities, and your budget, and choose the lens that works best for you.