Regarding the selection of the focal length of the CCTV lens, although only novices have this confusion, we still have to say it seriously.
It refers to the range covered by the monitoring CCTV lens. And the angles that can be seen on the monitoring screen. It is collectively referred to as the monitoring field of view.
When we normally purchase CCTV lens, besides the brand and how many pixels can be selected, there is also a choice of lens focal length.
Some pit-dealers will send you the default focal length of the CCTV camera, just because you do n’t understand. They are too lazy to explain it to you. When such a camera is installed, you will always find that the picture looks strange, but also said No problem! When a professional CCTV staff comes over, they will ask, how many focal length lenses do you buy? If you can’t answer it, then you are an unqualified “purchasing”!
Speaking of CCTV lenses, its imaging principle is the same as that of the human eye. It collects the reflected light of the illuminated object and focuses it on the CCD and projects it on the CCD. The image is inverted, and it is inverted by the camera circuit, which is the monitoring picture we see.
Generally, after you select a model of camera, there will be multiple focal lengths for you to choose. You choose a focal length according to the requirements and location of your camera.
The first purchase must have no specific concept on the focal length of the lens. The size of the focal length can determine the size of the picture, the size of the viewing angle range, and so on.
Places with small viewing distances and large viewing angles, such as elevators, ordinary rooms, and halls, use 2.8mm-4mm lenses. The monitoring distance is between 3 meters and 6 meters, and the viewing angle is between 70 ° -75 °.
For long distances and small viewing angles, such as narrow roads, corridors, and fences, 8mm-12mm lenses are usually used.
Outdoor places with large depth of field and wide viewing angle range, such as residential unit doors, warehouses, etc., usually use 6mm-8mm lenses.
In addition, the lens classification can also be divided into standard lenses with a viewing angle of about 45 ° -50 °, which is similar to the effect of the human eye; telephoto lenses, with a viewing angle of less than 20 °, have a larger focal length millimeter.
Pinhole lenses are only a few millimeters in diameter and are used for concealed installations, often mounted on ceilings, wall sockets, or small objects such as moving watches and lighters.
A zoom lens is a variable focal length lens that can be changed from wide-angle to telephoto. It is usually an electric type. Usually dome cameras are zoom lenses. They can be used as standard, wide-angle, and telephoto functions.
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