C1, TM 9-1240-318-35
Section II. DESCRIPTION AND DATA
description of each optic in the system is as follows:
a. Straight tube telescope M120 (fig. 1-1)
(1) Objective assembly.
The objective lens
M114A1E1 with 20 mm automatic gun M139. Straight
assembly (1 through 3, fig. 1-2) is a three element air
tube telescope XM134 (fig. 1-1) is used with both the
spaced triplet consisting of a double convex lens and an
gun, AAA, SP, 20 mm XM163 and gun, AAA, towed 20
air spaced doublet. A negative field lens (4) mounted in
mm XM167. The telescopes are the direct fire control
front of the reticle is also part of the objective system.
instruments used for positioning the weapon in deflection
Light passing through the objective forms an inverted
and elevation on targets visible from the weapon.
image of the distant object (target) at the reticle focal
Telescope M120 is mounted by means of a dovetail to a
bracket and secured with a locking device located on
mount, telescope M148. Telescope XM134 is secured
(2) Reticle. The reticle lens (5) serves as a
by the same method on mount, telescope XM164.
collective member to direct the field rays to the center of
the erector system, thus keeping the diameter of the
b. The external parts of the telescopes are the
erector lens to a minimum size. The reticle is a ballistic-
same. They are located and identified in figure 1-1 as
type with etching on the plane surface of a plano-convex
follows: A cap assembly (1) consisting of an optical glass
lens and is part of the erector system.
window in a flexible rubber cap, fits over the front end of
the telescope to protect the objective lens. A rubber
(3) Erector assembly. The erector assembly (6
eyeshield (2) fits over the rear end of the telescope to
through 9) consists of a double convex lens, two
protect the eye of the observer. A light well (for
cemented doublets, and a second double convex lens.
instrument light) (3) contains a threaded stainless steel
These lenses invert and revert the image (target) and
insert to accept the threads on the brass metal shield
project the erected image to the focal plane of the
containing the lamp socket of the instrument light. A cap
(4), used to cover the light well and prevent the entry of
dirt, moisture, etc., when the instrument light is not in
(4) Diaphragm. The diaphragm (13) acts as a
place, is fastened to the housing by a bead chain,
field stop by blocking light rays that are not essential to
secured by one of the screws holding the identification
plate. The dovetail mounting plate (5) is located directly
under the identification plate, secured by two socket
(5) Eyepiece assembly.
head screws and two steel pins to the telescope
assembly (10 and 11) consists of a cemented doublet
housing. Two screws (6), one located in front, and the
and a single element double convex eye lens. The
other located in back of the mounting plate, are used to
eyepiece serves to magnify the image (target) and reticle
close purging ports in the housing. After the assembled
telescope has been purged and charged with dry
nitrogen gas, these ports are sealed to eliminate
The window (12)
moisture which may damage internal optics and metal
allows light from the instrument light M52E1 to illuminate
the etching of the reticle.
The optical system (fig. 1-2) for both telescopes
d. Support equipment necessary for storage and
consists of the objective system, the reticle lens, the
operation of the telescope are as follows:
erector system, a diaphragm, eyepiece assembly, and
the optical components, with the exception of the reticle.
of molded, laminated, sheet plastic
are fluoride coated to increase light transmission through