文档介绍：Kottan-labs 5/21/2002
Introduction in Optics II:
II-1 Lenses
An optical lens is a piece of transparent material such as glass, quartz or
plastic. Because of its shape, however, light passing through it either
converges or diverges to its principal axis. The entire effect of the lens is due
to its shape and the index of refraction of the lens. Figure II-1-1 introduces a
(a) converging and (b) diverging lens. The focal length is the distance from
the focal point to the principal point. We assume that the thickness of the
lens material is negligible parison with the principal focal length and
any object and image distance. Such a lens of negligible thickness is called
thin lens. We consider only thin lenses here. For a thin lens, the focal length
isthedistancefromthefocalpointtothelens.
(a)
(b)
Figure II-1-1: (a) Converging and (b) a diverging lens.
The lens is called converging lens if all rays parallel and close to the
principal axis converge to the principal focus. A diverging lens is a lens that
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takes a bundle of parallel light rays and diverges them away from the
principal axis.
To determine the location of an image formed by a lens, we use the
technique of ray tracing. An object OP, represented by the brown arrow in
figure II-1-2, is placed a distance p in front of a convex lens. A ray, from the
bottom of the object at P, travels along the principal axis. This ray goes
trough the lens undeviated. Hence, the bottom of the image must lie
somewhere on the principal axis of the lens. To determine the location of the
tip of the image, three rays are drawn from the tip of the object. These rays
are called the standard rays and are shown in figure II-1-2.
Figure II-1-2: Ray diagram for a convex lens.
The first ray (1), in red, is drawn parallel to the principal axis and after
refraction it passes through the principal focus (2),ingreen,
is drawn from the top of the object and passes through the f