Automatic follow focus device based on video target tracking

The present invention discloses an automatic follow focus device based on video target tracking, which comprises: a cradle head, a cradle head motor, a cradle head motor driver, a distance measuring sensor used for measuring the distance from a movable target in real time and installed on the cradle head, a video collecting card used for receiving a video signal of a camera and outputting the video signal to a video terminal, the video terminal provided with video target tracking software in advance and used for receiving the video signal of the video collecting card and outputting coordinate values of a followed target relative to an image, a first lens motor and a second lens motor used for driving a focusing ring and a zooming ring of a lens, a lens motor driver used for driving the first lens motor and the second lens motor, and a main controller used for receiving a target distance value outputted by the distance measuring sensor and target coordinate values outputted by the video terminal and controlling the cradle head motor driver and the lens motor driver. The automatic follow focus device of the present invention has the advantages of automatic computation of field angles of the camera, no need of calibration and simple operation.