What does it mean to monitor the focal length in the camera?
Surveillance cameras are a lot of sellers don't understand the concept of focal length, they tell you that the lens is a few millimeters, this is a few mm focal length or the lens diameter they all don't understand, they only know to see far or near.
So, you have to look at the wider range, and you choose the small aperture lens, but the target is smaller.
Under normal circumstances, the fixed focus of surveillance cameras, the greater the size of the seller told, through the camera to see the target is big (that is, to read), but more narrow perspective (small observation range), the shorter the depth of field. The smaller the lens size, the smaller the target (i.e., the closer) the camera sees. The wider the Angle of view, the longer the field.
