Zoom lens

The longer the focal length of a camera lens, the further it is from the film (CCD) and the larger the image. Typical telephoto lenses are ~400 mm long. A zoom lens has two components - convex and concave. Adjusting the positions of the lenses independently, changes the focal length of the combination, and the size of the image. Schematic diagram.

High quality zoom lenses have 20 or more thin spherical lens components in two groups. The mechanical linkage is very complex. Image quality is not quite as good as that of the better fixed focus lenses, but amateur photographers, (and professionals in many circumstances), find the convenience outweighs the slight disadvantage. Next