Back focal length is to point to when installed on the standard lens, can make the subject of scenery image on the CCD image sensor of the target. Surveillance camera factory, pu throw or adjust for back focal length, the reason how the fixed focal length lens applications, most of the surveillance cameras back focal length adjustment do not require, in some applications, however, when the lens focusing ring adjust to limit position still may appear the phenomenon of image is not clear. At this point, in the case of clear lens interface is correct, you need to adjust surveillance cameras back focal length. According to the experience, in the vast majority of the surveillance cameras with electric zoom lens applications, basically all need to adjust the back focal length.

Methods to adjust back focal length as described below. Install the lens accurately to the surveillance camera. The lens aperture open as much as possible to the largest (purpose is narrowing the scope of the depth of field, in order to find correct imaging focus). Through zoom adjustment (ZoomIn) push the lens to telescopic (Tele) state, filming 10 m outside of the features of an object, again by adjusting the Focus (Focus) will feature the image clearer. In contrast to the previous step zoom adjustment (ZoomOut) the camera pulls back to Wide Angle (Wide) state, the images into a panoramic image with these feature objects, but this cannot be the focus adjustment (note: if the image change trance can't adjust focus), but prepare the next step after focal adjustment.

To use surveillance cameras front end after a fixed focal adjustment ring unscrew the Allen screw, the rotation and focal adjustment ring (no back focal adjustment ring of surveillance cameras to turn the lens and direct drive after its built-in JiaoHuan), until picture most clearly, and then tighten the Allen screw for the time being. Back the lens to the telescopic state, see if just shooting close-up objects are still clear, in the condition of telescopic, if features have clear object, tighten the Allen screw, adjust the aperture to the appropriate location, as you're done.