Before you purchase a new surveillance camera, it is important to think about the type of security camera lens that will best suit your needs. Focus lenses vary greatly, and so do the images that they produce. If you do not choose a camera with the right lens, you are unlikely to pick up the footage you were expecting. When you are in the security business and need to be sure that you capture useful images, this can be a serious problem.
You should consider several factors when you are deciding which focus lens will work for you. The first of these is focal length, which is measured in millimeters (mm). Generally, the shorter the length you choose, the wider the angle of view your surveillance camera will have. If you choose a greater focal length, your camera will have a narrower angle of view. For example, imagine that you have set up a security camera to take footage of the parking area in front of a building. If you are using a 3.6 mm lens from five feet away, you will be able to capture an image of the back of a parked vehicle along with its surroundings. With a 12 mm lens, you will only be able to pick up an image of that parked vehicle; however, you will easily be able to read its license plate number and identify any other distinguishing characteristics that it may have.
There is a formula you can use to help you decide which focal length is optimal for your situation. Simply multiply the security camera’s expected distance from an object by 4.8, then divide the result by the horizontal or vertical area that you want the surveillance camera to cover. For example, if you wanted to install a surveillance camera 20 feet away from an object and have it capture footage in an area that was five feet wide, you would make the following calculation:
20 x 4.8 / 5 = 19.2
In this case, you would want a focal length of 19.2 mm.
In addition to the focal length, you should think about the depth of field your surveillance camera lens can offer. If it has a large depth of field, your camera will bring almost every object within its field of view into focus. To achieve a greater depth of field, you should settle for a wide angle lens, use an auto iris, and have a high F stop.
Auto iris lenses are ideal for surveillance cameras that are placed outdoors, as they adapt well to changes in lighting conditions. (Manual iris lenses, which do not adapt to lighting changes, are in fact sufficient for cameras that are set up indoors.) A lens’s F stop is its ability to take in light when it is completely open (maximum aperture) and when it is about to close (minimum aperture).
The size of the CCD image device on your surveillance camera also plays a role in the quality of the images you capture. Surveillance cameras come equipped with 1/4-inch, 1/3-inch, 1/2-inch, or 2/3-inch chip sizes. The smaller your CCD chip, the narrower your camera’s angle of view will be.
Lastly, you should consider the size of the lens mount on your security camera. Mounts come in two standard sizes–“C, ” which measures 17.5 mm from the lens to the image sensor, and “CS,” which measures 12.5 mm. You might also consider whether you should use a video or direct drive, although almost any security camera can use either type.