The third important characteristic of telephoto settings: It is more difficult to focus in telephoto.

This is a fundamental rule of optics and there is no way to get around it. As the camera zooms in, focus gets more and more "critical." That is, it gets harder and harder to keep everything in focus.

Notice how only a small range of things are in focus in the telephoto shot to the right. The wheat in the foreground is out of focus—as is the wheat in the background. Only a narrow range is actually in focus.

In one sense, this makes life more difficult, because photographers want their subjects to be in focus. But this can also be used creatively, to lead the viewer to the items the filmmakers wants to emphasize.