The back focal length means that when installed on a standard lens (standard C / CS mount lens), the image can make the scene being shot exactly as the target surface CCD image sensor, the camera today to take you look back focal length of the camera case.
Usually the camera at the factory, on the back focal length are made appropriate adjustments, therefore, connected with fixed focus lens applications, generally we do not need to adjust the back focus of the camera. In some applications, it may appear still can not get a clear image when the lens focus ring to adjust the limit position, then you must first confirm that the lens interface is correct.
After the confirmation, you need to adjust the back focal length of the camera. According to experience, the vast majority of surveillance cameras connected with electric zoom applications often need to back focal length digital high-definition video camera to adjust.