Figure 8-28. Reflex sight.

TM 9-258

a. Condensing Lens. Light from a lamp or reflected

the image of the reticle are parallel, due to the action of

sunlight is concentrated on the reticle (para 4-9), usually

the collimating lens, the reticle pattern appears at infinity

by using a condensing lens or lens system. A frosted

which makes it possible for the observer to super-impose

surface (either one surface of the condensing lens or of

the image on the target and focus on both at once.

a plane glass plate) may be used to diffuse this light and

e. Use.

The reflex sight is a projection-type

obtain even illumination of the reticle. This light then

collimator sight used for direct sighting of machine guns.

passes through either a perforated reticle (usually

8-26. Aiming Circle.

punched in a metal disk) or illuminates a reticle pattern

a. The aiming circle (fig 8-29) is used to measure

etched on glass.

the azimuth and elevation bearing angles of a ground or

b. Collimating Lens. Light from the illuminated

aerial target with respect to a preselected base line. The

reticle passes through a collimating lens placed one focal

aiming circle has many of the characteristics of a

length from the reticle. The collimated light from the

surveyor's transit. Basically, it consists of a telescope

reticle is ordinarily introduced into the field of view by the

mounted on a mechanism which permits unlimited

use of a high-reflectance-coated glass plate which

azimuth and limited elevation movements. By rotating

permits light to pass straight through from one side but

two orientating knobs, zero azimuth heading with respect

reflects most of the light coming from the opposite

to magnetic north or any other selected compass

direction. A half-silvered mirror may perform the same

heading can be established. The azimuth orienting

function but less efficiently.

control knobs can be disengaged for rapid movement by

c. Parallax. To remove parallax from this type of

exerting an outward pressure on the knobs.

The

optical system, either the collimating lens or the reticle

mechanisms are spring-loaded and will reengage when

must be moved until the reticle pattern .s clearly defined

outward pressure is removed. A locking device secures

or sharply focused when viewed through the collimating

the compass after the orienting adjustment, has been

telescope.

made.

d. Operation. Since the reflected light rays from

8-28