The explanation that a lens’s focal length is the distance from the optical
center of the lens to its point of focus doesn’t tell the whole story, of
course. What is important is that the focal length determines the
relative field of view produced by a lens how wide or narrow its perspective
is. A lens with a wide perspective will provide an expansive view like the one
shown in Figure 1.10. One with an intermediate perspective (which photographers call normal) offers a view like
that in Figure 1.11. A narrow, telephoto view might bring details of a subject in very close, as shown in Figure
1.12.
