The zoom lens is a camera lens that can change the focal length within a specific range to obtain different field angles, images of different sizes and different scene ranges. The most prominent feature of the zoom lens, or its greatest value, is that it realizes that the lens focal length can be changed according to the photographer's wishes.
Unlike the fixed focal length lens, the zoom lens does not realize the lens focal length transformation by changing the lens quickly but by pushing, pulling, or rotating the lens's zoom ring. Within the lens zoom range, the focal length can be changed stepless. That is, any focal length within the zoom range can be used for photography, which creates conditions for the diversification of composition. The function of any level of the focal length of the zoom lens itself is the same as that of other fixed focal length lenses with the same focal length. However, the zoom lens does not limit which level of focal length the photographer uses, so it is much more convenient and flexible in use and operation. It saves the trouble of carrying and replacing multiple lenses with different focal lengths when shooting out. Even before pressing the camera shutter, the photographer can choose the subject and cut the picture by changing the lens focus to make the picture composition more ideal before shooting.
The speed of changing the focal length of a zoom lens is unmatched by changing the focal length of a fixed focal length lens. The zoom lens of a 35mm automatic pocket camera or some 35mm single-lens reflex camera also adopts the electric zoom mode. The electric zoom is labour-saving and convenient and realizes the average speed zoom, which is very beneficial for photographers to cut the picture and determine the composition through the slight change of focal length.
The zoom lens can also 'explode' by zooming when the camera shutter is opened. Some cameras also rely on automatically controlling the focal length transformation of the zoom lens to realize the automatic composition function. The latest 35mm single-lens reflective camera can also automatically memorizes the lens focal length, which allows the photographer to set the camera to memorize lens focal lengths with the high frequency of use and change the lens focal length to the previously memorized focal length at any time.
Of course, compared with the fixed focal length lens, the zoom lens structure is more complex, and the component is heavier. The imaging quality of non-famous zoom lenses is certainly inferior to the corresponding fixed focal length lens.