What is the meaning of monitoring the focal length in the camera?
Surveillance cameras sellers do not understand the concept of a lot of focus, they tell you that the lens is a few millimeters, the a few millimeters is the focal length or lens caliber they do not understand, they only know to see far or see close.
So, you want to see a wide range, to choose a small aperture of the lens, but to see the target will be smaller.
Under normal circumstances, the fixed focus of the surveillance camera, the seller told the larger size, through the camera to see the target larger (that is, look far), but the narrower the angle of view (observation range), the shorter the depth of field. The smaller the size of the lens, the smaller the target (see near), the wider the viewing angle (the viewing range), the longer the depth of field.
