Lesson 1/Learning Event 5
Learning Event 5:
IDENTIFY THE BASIC TYPES OF SINGLE LENSES
1. The purpose of a lens is to refract light rays to a sharp, clear image.
Camera lenses are designed to function with the least amount of error and to
reproduce objects in a practical object-image size relationship (fig 1-12).
Pinhole lenses are not practical for general photography as the size of the
pinhole must be very small to produce a nearly clear, focused image. Due to
the size of the pinhole, a long exposure time is necessary to expose an
image.
Figure 1-12.
The pinhole camera
2. A camera lens is a polished spherical and symmetrical glass that
refracts light rays from an image of an object to the rear wall (focal
plane) of the camera. A lens transmits more light that a pinhole, producing
an increase of brightness and an improvement of image sharpness (fig 1-13).
Figure 1-13.
The simple camera
3. Types of Single Lenses.
There are two general categories of single
lenses: positive and negative.
a. Positive lenses are convex on one or both surfaces and bend light
rays towards its center (fig 1-14).
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