CCTV镜头选择工具，通过监控范围来选择合适的镜头焦距。也可通过镜头的焦距，以及镜头跟监控目标的距离，来计算出视频的范围。-CCTV lens select tools.it use to select the focus of the lens by monitoring Area.also can counter the area of video by focus and distance.