The principle of cine zoom

The principle of cine zoom is to adjust the lens focal length and move the camera position in reverse synchronization to change the perspective relationship of the picture, while keeping the subject size constant. Specifically, it can be divided into the following two technical paths:
Optical zoom principle
By moving the positive lens to change the focal length, for example, the optical components inside the zoom lens move with the change of focal length to maintain the stability of the central body size of the image.  ‌
Principle of mechanical zoom
Taking Hitchcock zoom as an example, the focal length is reduced when the camera is moved forward at a constant speed (or increased when moved backward) to counteract the size changes of the subject in the image. Accurate matching of the movement speed of the camera position and the focal length adjustment speed is required, usually with the help of stabilizing equipment to ensure that the subject is always at the center of the screen.  ‌