Projection Devices, Continued
The overhead projector is a simple device. It consists of a three-position
on/off switch, a lamp, a fresnel lens, mirrors, a projection stage, a focusing
knob, a blower, and a condenser. The fresnel lens is the key component of
an overhead projector. This prismatic lens is a series of concentric circular
scribes calculated to concentrate and intensify the light, as it passes through
the visual onto a mirror.
Figure 5-4 shows the elements of an overhead projector.
Figure 5-4. Overhead projector nomenclature.
Continued on next page