Figure 8-25. Range finder , tank (typical coincidence type).

TM 9-258

b. Characteristics. This typical coincidence-

patterns, and reticle illumination system of the range

finder are treated separately. Component parts of each

type range finder measures 85 x 14 x 12 inches overall,

system are individually described to define their

weighs 149 pounds including end housing assemblies,

functional purpose.

has a range of 500 to 4400 meters, and a field of view of

NOTE

The key numbers shown in parentheses

The key letters shown in parenthesis

refer to figure 8-23.

in c and d below, refer to figure 8-23.

c. Theory of Operation.

(2) Left optical system. The left optical

(1) Light from a target enters the range finder

system consists of an end housing assembly, a main

through the right and left end housings. There is a

sighting system, and a collimating system. A target

definite parallactic (convergent) angle between the light

image picked up at the end housing assembly is

entering through one end housing window from the target

transmitted into the main sighting system. A coincidence

and light entering through the other end housing window

reticle image projected from the collimating system is

from the target. This parallactic angle varies with target

also projected in this main sighting system. These

distance, being larger for close targets than for distant

images merge with the gunlaying reticle and are

targets. The optical system (fig 8-23i utilizes this

transmitted to the eyepiece which is common to both the

parallactic angle variation as a means of measuring

left and right optical systems.

target range. This is accomplished by displacing a

(a) End housing assembly. The target image is

specially designed lens a calibrated distance in order to

picked up by the end housing assembly and turned 90

deviate the light through the parallactic angle and

degrees for introduction into the left main sighting

establish coincidence of the target at the eyepiece.

system.

(2) Light rays, upon entering each housing

1. The end housing window (1) is a plano plate,

window, are reflected 90 degrees toward the center of

the range finder. These light rays enter the telescope

that seals the end housing against dirt and moisture.

2. The end housing penta reflector (2) provides

optical systems and, after passing through the lenses

and being reflected by the prisms, leave the instrument

a constant deviation of 90 degrees. The penta reflector

by way of the single eyepiece. Light rays from the

is adjustable to correct for tilt and deviation.

3. The end housing corrections wedge (3) on

internal collimator optical system are projected to the

telescope optical systems by means of reflectors.

the inboard end of the housing may be used to correct

Images formed at the eyepiece diaphragm are a

deviation due to initial misalignment of the penta reflector

composite of a target image and the image of the

or housing. The wedge also serves as a window, which

internal collimator optical system coincidence reticles for

seals the end housing against dirt and moisture.

both the right and left side optical systems.

4. The end face of the housing casting is

d. Functional Description.

precision machined. Alinement keys are used to position

(1) General. For purposes of description, the

the end housings to the main housings.

left optical system, the right optical system, reticle

(b) Left main sighting system. The left main

sighting system carries the target image from

8-22