Left optical system

TM 9-258

the left end housing assembly to the eyepiece. The left

three correction wedges (19, 20, and 21). The vertical

main sighting system is housed in both left and right

calibration mechanism optical components consist of two

main housing castings.

correction wedges (19 and 20). A gear located between

1. The range finder end window (4) is a plano

the two wedges causes these wedges to rotate in

opposite directions.

Light rays entering the first

plate, which seals the left sighting system against dirt

correction wedge (19) are bent towards the thickest part

and moisture.

2. The filter (5) increases contrast between the

of this wedge. Due to the relationship of the thick

sections, a vertical vector resultant is formed which

target image and the illuminated coincidence reticle (49).

optically raises or lowers the light rays. The horizontal

A matched filter (26) for the right main sighting system is

calibration mechanism consists of a single correction

engaged simultaneously with the left filter by a control

wedge (21). This correction wedge receives the light

lever on the right main housing.

rays from the second correction wedge (20) of the

3. A porro reflector assembly (6) and (7)

vertical calibration mechanism. As the horizontal wedge

consisting of a partial reflector (7) and a full reflector (6)

is rotated, light rays are deviated in a horizontal direction.

bends the coincidence reticle image 180 degrees to

8. The first 90-degree prism (50) reflects the

superimpose it on the target image. The partial reflector,

target and reticle images into the second erector lens

in the line of sight of the main sighting system, picks up

(51).

the coincidence reticle image from the full reflector,

9. The second erector lens is used to set the

which picks up the image from the left collimating

focus during the assembly of the range finder, and to

system. The path of the target image is not affected by

bring the focal plane of the left main sighting system to

the partial reflector. Approximately 65 percent of the

the eyepiece field stop (42).

incoming field light is transmitted through the partial

10. The second 90-degree prism '52) bends the

reflector, 30 percent is lost by reflection and 5 percent is

light rays into the left ocular prism (46).

lost by absorption. Less than 30 percent of the light from

11. The left ocular prism (46) is a penta prism

the collimating system is transmitted into the line of sight;

70 percent of the light passes through the partial reflector

that reflects the target image 90 degrees into the

and is lost. However, collimator light intensity can be

combining prism (45).

12. This combining prism displaces the light rays

varied by a rheostat.

4. The left objective lens (8) receives light from

parallel to itself. The light rays are then reflected into the

the target and coincidence reticle, and provides a focus

eyepiece assembly by the rhomboidal prism component

adjustment. Light rays from the left objective lens (8) are

of the combining prism.

assembly.

converged upon the first collective lens (15) and are

The eyepiece

brought into focus at the main boresight (gunlaying)

contains a field stop and an eyepiece assembly. The

reticle (16). Moving the collective lens adjusts the focal

field stop (42) is a diaphragm for the eyepiece assembly.

length to the' desired angular values of the reticle

It restricts extraneous or stray light for a sharp circular

calibrations. The left objective lens and the first collective

field of view. The eyepiece assembly has a field lens

lens function together as a single lens.

(43) and an eye lens (44), which together magnify the

5. The main boresight reticle assembly

image.

(d) Left collimating system. The left collimating

contains the main boresight (gunlaying) reticle (16).

Because it is in the focal plane of the objective lens (8)

system projects the left coincidence reticle into the left

and the first collective lens (15), this reticle is

main sighting system so that the coincidence reticle

superimposed on the target image. Control knobs move

appears in the field of view.

the boresight reticle vertically and horizontally to aline it

1. The left coincidence reticle (49) is

with the target image for boresighting, range estimation,

illuminated and projected into the collimator lens (13).

or both. The main boresight reticle assembly has a

2. The collimator lens (13) gathers the

collective lens (15 and 17) on each side of the reticle

diverging light from the reticle assembly and directs it,

(16) to increase the field or peripheral light.

with the coincidence reticle image, into the porro reflector

6. A composite image of the reticles and target,

assembly (6 and 7).

formed by the second collective lens (17), is located at

3. The collimator assembly contains two

the focal plane of the first erector lens (18).

correction wedge cell assemblies, each containing a

7. The target and reticle images are positioned

wedge (9 and 10) that alines the coincidence reticle in

vertically

and

horizontally

series

deflection and elevation so that it is projected in an exact

relationship to the target image as seen in the main

sighting system.

8-23