Why can't a photographer choose a large zoom lens to go all over the world like taking pictures in film and television shooting?

The shortcomings are also obvious. The aperture is too small (the numerical value is 3.5) and mostly floating, which means that the aperture will shrink when the focal length is long. Take Canon 18/ 135mm as an example. When the focal length is 135mm, the maximum aperture is only 5.6f.

At any given focal length, its imaging is often not as clear as the best fixed-focus lens. Forget about these birth defects. Today's optical industry uses computers to design lenses and produces many excellent zoom lenses. Many zoom lenses are very clear and small in size, but the price is still very expensive. When using zoom lens to focus, it is best to adjust the image to the maximum position first; In other words, the longest focal length end of the lens is used for focusing. Then, reduce the focal length to the desired focal length when shooting. In this process, the images of all focal lengths are always clear.

Using this technology, it is easier to observe whether the image details are clear because it focuses on the image as large as possible, so it is also the most accurate focusing method. Note that some zoom lenses need to rotate two independent control rings, one ring controls the focal length and the other ring controls the focal length. The advantage of this structural layout is that once the focus is completed, the focus will not be unexpectedly changed by adjusting the focus. Other zoom lenses only need to move a control ring, turn to focus, and slide back and forth to change the focal length. This kind of "single ring" zoom lens is often faster and easier to operate, but it is usually more expensive. When changing the focal length, be careful not to lose the clear focus.