TM 11-6730-235-35
CHAPTER 2
FUNCTIONING
d. The light rays that pass through the image
2-1. General
source are collected by a bottom lens in the lens
a. This chapter describes the functioning of the
head assembly. This lens condenses the light rays,
projector.
focusing them at a point that lies behind a mirror
in the lens head assembly.
b. The description is presented under the fol-
lowing categories:
e. The mirror reflects the image-containing
light rays. The reflected light rays strike a front
(1) Optical-mechanical operation (para 2-2).
lens in the lens head assembly.
(2) Electrical operation (para 2-3).
f. The front lens diverges the reflected light
rays. This divergence magnifies the image to
2-2. Optical-Mechanical Operation
impose it on the projection surface.
The projector is an optical device in which control
of certain optical functions is accomplished by the
g. The lenses and the mirror in the lens head
operation of mechanical elements. The optical
assembly pivot as a unit under the control of the
elements of the projector and the related mechani-
operator. This pivoting action changes the angle of
cal elements are shown in schematic form in figure
incidence of light rays from the image on the
mirror. Changing the angle of incidence, in turn,
changes the angle of elevation of the projected
a. A projection lamp located in the lamp hous-
image. When the angle of elevation is changed, the
ing assembly of the projector case assembly is the
projected image is moved up or down in
light source for the equipment. A reflector located
accordance with the angle of the pivoting action.
directly below the lamp shapes the light into a
beam. This beam is directed toward a fresnel lens.
h. The lens head assembly is fixed to a pinion
gear in the focusing arm holster of the arm and
b. The fresnel lens is a two-element plastic
post assembly in the projector. This pinion gear lies
plate which consists of a number of concentric
on a shaft that passes through the two focus knobs
circular lenses arranged around one common lens.
of the projector. The teeth of the pinion gear mesh
The fresnel lens collects light rays with many
with teeth on a rack that is located on the post of
angles of incidence to bring them to a point of
the projector arm and post assembly. Turning the
common focus. The light rays being focused by the
focus knobs turns the pinion gear. Turning the
fresnel lens pass through a stage glass.
pinion gear moves the gear up and down the post.
The direction of motion is determined by the
c. The stage glass is a transparent sheet of glass
direction in which the focus knobs are turned.
that is used as a support for the transparency that
contains the image to be projected. This image
i. When the lens head assembly moves up or
consists of a combination of translucent, opaque,
down, the distance between the image source on
and partially opaque areas. Light rays from the
the transparency and the lens system in the lens
fresnel lens pass through the stage glass and the
head assembly is changed. Changing this distance
image source with an intensity and color that is
changes the point at which the projected image
determined by the transparency and color of the
is focused.
image source.
2-1
