Lens is the eye of security camera, it's one of the most important part of a security camera.  

Do you know how to choose lens to achieve different surveillance purpose? Such as see human face, human body contours or human activities? If not, please refer to below table:

"n" represents focal length of lens, such as 3.6mm, 6mm,12mm etc. For example, a 2MP/1080P IP camera,with 6mm lens. The calculation result as below:

* See the face/car plate clearly at 9m(1.5*6m);

* See the body contours at 18m(3*6m);

* See human  activities at 36m(6*6m).

The 9m, 18m, 36m is distance from scene to camera.