The external structure of the lens usually includes five parts: lens, zoom ring, focus ring, focal length scale and lens mount. The zoom ring can change the focal length of the lens to obtain different viewing angles. Only zoom lenses have zoom rings, and fixed-focus lenses do not have this component.
Function
The function of the zoom ring is to change the focal length of the lens. In other words, adjust the zoom ring to change the perspective of the photo, the size of the subject being photographed, and the perspective relationship between each subject.
Usage
To change the perspective of the photo, the size of the subject being photographed, and the perspective relationship between each subject, photographers need to manually adjust the zoom ring.
Please note that lenses with distance scales and lenses without distance scales have different positions for focus rings and zoom rings. Please refer to the figure above for details.
Depth of field is controlled by three factors: focal length, aperture, and distance between the subject being photographed and the lens. Therefore, depth of field is controlled by zoom rings, aperture rings, and focus rings together.