(1) Wide angle, or short focal length lenses.
(2) Normal, or medium focal length lenses.
(3) Narrow angle, or long focal length lenses, often called telephoto
lenses.
(4) Zoom, or variable focal length lenses.
b. The wide angle or narrow angle refers to the field of view, the
relative vista of the lens.
The "short" and "long" refer to the actual
focal length (fig 2-1) the distance from the optical center of the lens
(often the midpoint between the front and back lens elements) to the point
where the distant image as seen by the lens is in focus.
(1) With a wide angle lens, or short lens, you can see more; you have
a wider vista. Objects very close to the lens appear quite magnified, but
the ones just a little farther back look rather small. A short lens creates
an effect similar to looking through binoculars the wrong way.
(2) With a narrow angle lens, or long lens, you have a narrower
vista, but what you see, even the distant objects, are greatly magnified. A
long lens is similar to binoculars used correctly.
(3) The normal lens gives you the view of the normal human vision.
Figure 2-1.
Focal length
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