Difference between zoom ring and focus ring of camera

Focusing is to move the position of the equivalent lens to make the scene image on the film; Zooming is to change the focal length of the equivalent lens. There is no relationship between the two.

All zoom lenses are designed to zoom without changing the focus position, that is, the subject position is fixed. After the photographer position is fixed, you only need to focus once, and then you can change the focus at will without refocusing.

Focusing the lens to the longest focal length is because the viewing angle is the smallest at this time, and whether it is manual or automatic, the position of the focal point can be determined more accurately.