What is the "swing" of the lens in the movie?

Clapping is a popular saying that the lens is exposed with the moving object.

Because the object is moving, if the ordinary exposure method is used, the picture presented by the object in the photo will be blurred because the moving speed of the object exceeds the speed of the camera shutter.

Therefore, in order to keep the exposure speed of the object consistent with the shutter speed of the camera, the lens follows the moving object when shooting, so that the relative speed between the lens and the photographed object is zero, so that the photographed moving object will be clear, which is generally used in sports photography, animal photography and a small amount of breaking news.