    [Field Glass, Type Ee]
    [From the U.S. Government Publishing Office, www.gpo.gov]

    ﻿1.35: <=/-iipll ]TM 9-1611

    Document Reserve
    WAR DEPARTMENT
    TECHNICAL MANUAL

    ORDNANCE MAINTENANCE
    FIELD GLASS, TYPE EE
    April 7, 1942
    NON-CIRCULATING
    NTSU LIBRARY
    *TM 9-1611
    TECHNICAL MANUAL No. 9-1611
    WAR DEPARTMENT, Washington, April 7, 1942.
    ORDNANCE MAINTENANCE
    FIELD GLASS, TYPE EE
    Section I. General.	Paragraph
    Scope___________________________________________ ]
    II.	Description and operation.
    Genera]_________________________________________ 2
    Components______________________________________ 3
    Salient characteristics_________________________ 4
    Optical characteristics_________________________ 5
    Specific characteristics________________________ 6
    Operation_______________________________________ 7
    III.	Inspection and correction.
    Purpose_________________________________________ 8
    Inspection report_______________________________ 9
    Preliminary inspection_________________________ 10
    Double vision__________________________________ 11
    Parallax_______________________________________ 12
    Diopter scale__________________________________ 13
    Interpupillary distance scale__________________ 14
    Position of reticle_______________________:__ 15
    Appearance of scales and exterior finish_____	16
    IV.	Maintenance and repair.
    General________________________________________ 17
    Facilities necessary for making corrections__	18
    Double vision__________________________________ 19
    Parallax_______________________________________ 20
    Diopter scale__________________________________ 21
    Interpupillary distance scale__________________ 22
    Position of reticle____________________________ 23
    Appearance of scales and exterior finish_____	24
    V. Disassembly and assembly.
    Precautions____________________________________ 25
    Disassembly of objective (right or	left)_____	26
    Disassembly of eyepiece from body______________ 27
    Disassembly of right eyepiece__________________ 28
    Disassembly of left eyepiece___________________ 29
    *This manual supersedes TM 9-1611, September 12, 1941.
    449349°- 42-----1
    1
    TM 9-1611
    1—2	ORDNANCE MAINTENANCE
    Section V. Disassembly and assembly—Continued.	Paragraph
    Disassembly of body (right or left)________ 30
    Disassembly of right body from left body___	31
    Removal of stop_______________________________ 32
    Precaution for assembly_______________________ 33
    Assembly of objectives (right or left)________ 34
    Assembly of right eyepiece____________________ 35
    Assembly of left eyepiece_____________________ 36
    Assembly of body______________________________ 37
    VI. Care and preservation.
    Care in handling______________________________ 38
    Lubrication___________________________________ 39
    Care of optical parts_________________________ 40
    Page
    Appendix. List of references_________________________________ 24
    Section I
    GENERAL
    1.	Scope.—This manual is published for the information and guidance of ordnance maintenance personnel. It contains detailed instructions for inspection, disassembly, assembly, maintenance and repair of the glass, field, type EE, supplementary to those in the Field Manuals and Technical Manuals prepared for the using arm. Additional descriptive matter and illustrations are included to aid in providing a complete working knowledge of the materiel.
    Section II
    DESCRIPTION AND OPERATION
    Paragraph
    General_______________________________________________________________ 2
    Components------------------------------------------------------------ 3
    Salient characteristics----------------------------------------------- 4
    Optical characteristics----------------------------------------------- 5
    Specific characteristics---------------------------------------------- 6
    Operation-------------------------------------—----------------------- 7
    2.	General.—a. The field glass is an optical instrument used for observation and approximate measurement of small horizontal and vertical angles. A field glass is essentially two terrestrial telescopes mounted together for binocular vision. It is constructed in two halves, each carrying a compact prismatic telescope. They are
    2
    TM 9-1611
    2-4
    FIELD GLASS, TYPE EE
    pivoted about a common hinge to provide adjustment for changing interpupillary distances to suit the eyes of the user.
    b. Glass, field, type EE, is the limited standard glass for issue to the using arms. Field glass, type EE, of U. S. naval gun factory manufacture is also limited standard.
    3.	Components.—a. The instrument complete consists of— Glass, field, type EE.
    Case, carrying.
    Strap, neck.
    Strap, carrying case.
    b. These four components are illustrated in figure 1.
    I *jl» * «. w V " ^^aBbgtf&Bh
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    RA PD 5631
    1. Carrying case.	3. Carrying case strap.
    2. Neck strap.	4. Field glass.
    Figure 1.	—Glass, field, type EE (complete).
    4.	Salient characteristics.
    Magnification______________________________________ 6X
    Field of view______________________________________8°
    Apparent field of view______________________________48°
    Diameter of objective lens__________________________30 mm.
    Diameter of exit pupil______________________________0.197 in.
    Effective focal length of objective_________________ 4.890 in.
    Effective focal length of eyepiece__________________0.811 in.
    3
    TM 9-1611
    5
    ORDNANCE MAINTENANCE
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    1.	Eye guards.
    2.	Focusing nuts.
    3.	Hinge pin screw.
    4.	Body.
    5.	Objective cell.
    6.	Rear body cover.
    7.	Interpupillary scale.
    8.	Diopter scale.
    9.	Hinge pin.
    distance
    Figure 2.	—Glass, field, type EE.
    5.	Optical characteristics.—a. (1) Each half of the type EE field glass is a terrestrial telescope employing Porro prisms as the erecting mechanism. An examination of figure 3 will show how this is accomplished. The baton and arrow represent an image in the field of view which has been inverted and reversed by the objective lens. It will be noted that the baton is again reversed by the horizontal prism while the arrow is reinverted by the vertical prism.
    (2	) Porro prisms not only erect the image but also greatly reduce the length of the telescope and provide a means of adjustment. Furthermore, they are so arranged as to separate the objectives of the two telescopes considerably more than the eyepiece, thus increasing the stereoscopic effect.
    Z>. All modern military field glasses are constructed for separate focusing; that is, each eyepiece is focused independently of the other by screwing it in or out. Strictly speaking, a change of focus is necessary whenever the distance of the object viewed changes. However, with modern field glasses, when the instrument is focused for an object at average range, objects at all but very short distances can be seen at substantially their maximum distinctness.
    4
    TH 9-1611
    6
    FIELD GLASS, TYPE EE
    /I	zX]	cjl
    VERTICAL PORRO / ///	//////	kJ
    PRISM \	/r	I	—     ---
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    /	।	// ^-HORIZONTAL PORRO PRISM
    v^ fefii «sa
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    , .'■■■. : ■ ' '■ ' ■ . . ■■■ ■ ■ -■ ■ '■■;
    w
    L ■'-'	RA PD 5632
    1.	Surface plate and testing fixture.
    2.	Surface gage and special fixture.
    3.	Collimating telescope.
    4.	Telescope adapter.
    5.	Field glass.
    6.	Level.
    7.	Field glass holder.
    8.	Telescope holder.
    Figure 6.—Adjusting fixtures.
    12
    TM 9-1611
    18-19
    FIELD GLASS, TYPE EE
    •- 5“-•
    —
    ■ • ■ r
    |I , I[|I J k !||!,|“1^
    RA PD 5628
    Figure 7. Testing target for field glasses.
    19. Double vision.—a. To correct double vision the two optical axes must be made parallel to each other and to the mechanical axis of the instrument. When the interpupiUary distance is set at 64 millimeters, the optical axes of both telescopes must be parallel within i/2 mil. both vertically and horizontally, to one another and to the mechanical axis of the hinge joint.
    6.	Locate the special target at a distance of 139 yards and approximately level with the testing fixture. This distance must be exact because the dimension (21^ inches) indicated in figure 7 is equivalent to 1/2 mil at 139 yards. A 100-foot measuring tape is provided on instrument repair truck Ml. The target may be leveled, and the vertical line on the testing target rendered accurately perpendicular by use of the plumb line. Mount the collimating telescope in the telescope adapter and the telescope adapter in the clamping device on the testing fixture. Adjust the adjusting fixture by means of the leveling screws so as to bring the intersection of the cross lines of the collimating telescope reticle into coincidence with the point on the testing target indicated by the diamond (fig. 7). Remove the collimating telescope from the adjusting fixture and mount it in the
    13
    TM 9-1611
    19-20
    ORDNANCE MAINTENANCE
    telescope holder on the surface gage, as shown in figure 6. With the surface gage pins against the edge of the adjusting fixture and the right hand pin against the stop pin indicated by the 1.2-inch dimension in drawing C49109, adjust the collimating telescope until the cross lines of the reticle coincide with the cross lines on the testing target.
    c.	Set the field glasses to an interpupillary distance of 64 millimeters by means of the interpupillary scale. Clamp the field glasses in a level position relative to the leveled surfaces plate. Place the surface gage against the stop pin for the right eyepiece of the field glasses and, sighting through the collimating telescope into the eyepiece, focus the eyepiece until the image appears sharp and clear. Adjust the Porro prism by means of the special headless, cone-point adjusting screws until the circle on the testing target is in coincidence with the cross lines of the collimating telescope reticle. Repeat this operation with the left telescope until a similar condition is obtained on the corresponding left section of the target, the square.
    d.	Any apparent tilt in the field of view can be similarly corrected by adjusting the headless cone-point tilting screws until the tilt is eliminated.
    e.	(1) To adjust the Porro prisms nearest the objective ends, use the four headless cone-point screws (A36195) arranged in a plane around the body. The prisms may be shifted or rotated slightly in position by proper movement of the screws.
    (2) To adjust the Porro prisms nearest the eyepieces use the two remaining headless cone-point screws. These move the Porro prisms diagonally up toward the center of the instrument or down and away from the center.
    (3) When adjusting the Porro prisms, always be sure to loosen the opposing screws before tightening up the screws shifting the prism in the desired direction. This avoids the danger of chipping or straining the prisms. In most cases the total adjustment required will be very small.
    20.	Parallax.—a. Parallax may be eliminated in one of several ways:
    (1)	The reticle may be moved to coincide with the focal plane of the objective.
    (2)	The focal plane of the objective may be so shifted as to coincide with the reticle.
    (3)	A combination of (1) and (2) may be used.
    14
    TM 9-1611
    20
    FIELD GLASS, TYPE EE
    Z>. Preliminary.— (1) To make these adjustments it is first necessary to determine how much and in what direction the correction is to be applied. To determine this, place the instrument in the fixture (fig. 6) in a horizontal position, with both of the eyepieces level in relation to each other. Put the collimating telescope in the surface gage holder and place it in front of the left eyepiece. Then obtain clear and sharp definition of an object at least 100 to 200 yards away by use of the collimating telescope.
    (2) Note the reading of the diopter scale when this has been done. Assume that it is minus five. Next focus the eyepiece until the reticle is sharp and clear as seen through the collimating telescope. Note the reading of the diopter scale when this has been done. Assume that the reading obtained is minus three. This difference in the two readings would indicate a difference of sharp definition of the reticle in relation to sharp definition of the field of view of two diopters. It follows that this is the amount of parallax present. The tolerance permitted for the difference in readings is 1/2 diopter. There is present (in this hypothetical instance) undesirable parallax in the amount of two diopters which must be eliminated.
    (3) lo eliminate it, the focal plane of the objective must be shifted two diopters to coincide with the reticle, or the reticle must be shifted two diopters to coincide with the focal plane of the objective.
    c. Methods of moving focal plane of objective by interchange of parts to coincide with reticle.— (1) Interchange the objective lens cells from right to left (or vice versa) if they show an obvious difference in length.
    • (2) Try a new objective cell with a difference of length in the desired direction.
    (3) Try a different adapter.
    d.	Methods of shifting reticle by interchange of parts to coincide with focal plane of objective.—(1) Change the reticle cell for one of different size.
    (2)	Change the eyepiece sleeve.
    (3)	Change the eyepiece washer.
    (4)	The eyelens cell may be screwed in or out slightly to give a longitudinal displacement of image.
    (5)	Interchange eyepiece assemblies.
    e.	Methods of interchanging or replacing optical elements to obtain either of results outlined in c and d above.—Optical components would not ordinarily be changed unless replacement was the only
    15
    TM 9-1611
    20	ORDNANCE MAINTENANCE
    alternative clue to breakage, or for other reasons affecting the final condition of the field glasses.
    (1)	Effect of replacing the objective lens.— («) The use of a new objective lens with a focal length longer than the original will move the focal plane in a plus direction and increase the diopter reading on the minus side.
    (7?) The use of a new objective lens with a focal length shorter than the original will move the focal plane in a minus direction and increase the diopter reading on the plus side.
    (c) In changing objective lenses only the focal plane of the objective is moved in relation to the reticle. Changing the objective lenses will not affect a change of the diopter scale reading on the reticle.
    (2)	Effect of changing Porro prisms.— (a) If a prism is replaced by one that is larger than the original, the focal plane of the objective will be moved in a minus direction.
    (Z>) If a prism is replaced by one smaller than the original, the focal plane of the objective will be moved in a plus direction.
    f.	Methods of moving image in relation to eyepiece by machine work on metal components.— (1) After all the forementioned procedures have been tried and exhausted, the machining of metal parts may be considered. Machine work should always be done on the cheapest part insofar as practicable, if satisfactory results can be obtained by so doing.
    (2)	The objective cell may be shortened in length to move the focal plane of the objective lens in a plus direction.
    (3)	The shoulder on the inside of the objective cell may be machined to move the focal plane of the objective lens in a minus direction.
    (4)	The objective cell adapter may be machined to move the focal plane of the objective in a plus direction. Machining should be done on the inside shoulder.
    (5)	Use of a thicker objective cell adapter will move the focal plane of the objective in a minus direction.
    (6)	The shoulder on the reticle cell may be reduced when it is desirable to move the reticle in a plus direction to coincide with the focal plane of the objective without changing the diopter reading of the field of view.
    (7)	The shoulder on the eyepiece sleeve may be machined to move the reticle in a plus direction without changing the diopter reading of the field of view.
    16
    TM 9-1611
    21-24
    FIELD GLASS, TYPE EE
    21.	Diopter scale.—a. If the diopter movement is correct and only the reading of the scale is in error, it can be adjusted by loosening the diopter scale lock screw and moving the scale around independently of the focusing nut until the zero registers opposite the index. This will in no way change or interfere with the diopter movement or affect the optical characteristics of the instrument. The only thing that has been done is the shifting of the scale relative to the index.
    b. The above method of correction, however, should only be employed for small changes. When a change of three or more diopters is required, the focusing nut should be shifted by using the sextuple thread.
    22.	Interpupillary distance scale.—a. Remove the eye guards from both eyepieces. No further disassembly of the instrument will be required.
    b. Measure from the outside of one eyepiece to the inside of the other. This is preferable and much more accurate than attempting an approximate measure from the center of the eyepiece, and the same result is achieved.
    _____________________________________________	________
    RING - A36I8I-	V —	f	>—	\
    0BJECTIVE-A36I79-,	----------/ |TXT	I--1	I--1	XXXXX>
    CELL -A36I78-1	/ |,----------------UH------JUj---— ’	m	---------------------------------
    \ St
    "“((jp--------! SCREW-A36I89	I--1	I-- i-SCREW-A36I99
    h	\ X	f RING-A36I88---	SCREW-A36207-I Hj________________[J L_SCREW-A36205
    \ /	V *L	—__J	GUARD-A36I87-	RING-A362I0- LpiN-A362ll	--SCALE-816451
    L--\/	J/ .L-—^-r-——y-^l	CELL-A36I82-- -----------------------------------------------------------ST0P-A36202
    p' '	—— y SPACER-A36I85--------------------	SECTION A-A	r—SPRING-A36200
    ^OBJECTIVE, ASSEMBLY-C44148	C0VER-BI6448—।	EYELENS - A36I83- _	rSCREW-A36I97
    PRISM-A36I94—1 WASHER - A36209  EYEPIECE,ASSEMBLY-C44I47	-—|T]-----p	I l~L7^3~
    SECTION D-D-D	SCREW-A36I98	(jl	<	c?
    SCREW-A36I99---	-----—SCREW-A36I95 / / L	___<3 E
    CLIP-A362OI-- pBODY - D982O	------WASHER - A36209	___ .—-i	/	/ L-Ll\	[
    COVER-BI6449-J	C0VER-BI6450------ -------LENS-A36I84
    [— RETAiNER-B'MAi	--	OB
    [T / iLiCa fl r-SLEEVE- A36I9O	B—<^- ^9	ENLARGED SECTION B-B
    JuB -FO,	1w
    l\	~	~~'	|\ ’ny —SPACER-A36I85	p     -p,	-—	I	k
    __I '\A * I ji JiW_______________ jfyr------eyelens’a36183 I_______________________° p-] V _	IU-—rO,: — ] Vl—r—	;----CELL-A36I82 ----- _______________________ V
    S	—RING-A36I88	\
    EYEPIECE, ASSEMBLY-C44I46 J CELL-A36I9|J	IsCREW-A36I89^*
    RETAINER - BI6445- SPACER-A36I92-1 LRETICLE-BI6444	----U-----------fra szi
    SECTION C-C	~
    Figure 8.—Field glass, type EE—assembled and sectional view.
    19
    TM 9-1611
    25-29
    ORDNANCE MAINTENANCE
    replacement of even one optical element may change the optical characteristics of the telescope and render readjustment necessary. Replacement of metal components is easily accomplished since the components are all standardized and available as replacements. Keep in mind, however, that the replacement of such components as the objective cells, objective adapters, reticle cells, etc., may cause parallax and affect the final adjustment of the instrument. The greatest of care and considerable thought must therefore be given to the replacement of any part.
    26.	Disassembly of objective (right or left).—Before removing the objective assembly, mark the location of the cell with respect to the adapter, and of the adapter with respect to the cover. Unscrew objective cell (A36178, fig. 8) using a strap wrench if necessary. The objective cel] is held to the body by the objective adapter (A36177). The objective adapter may or may not unscrew with the objective cell. If it unscrews with the objective cell, unscrew it from the cell. Unscrew the retaining ring (A36181). Remove the objective lens from the cell.
    27.	Disassembly of eyepiece from body.—Scribe a reference line on the body cover (B16448 or B16450) to coincide with the engraved line on the eyepiece sleeve. Unscrew the eyepiece from the body. Remove the eyepiece washer (A36209) from the body cover.
    28.	Disassembly of right eyepiece.—Unscrew the eye guard (A36187) from the eyepiece. Unscrew the eyelens cell (A36182) from the focusing nut (B16442). Unscrew the diaphragm (A36186) from the eyepiece sleeve (A36190). Unscrew the eyepiece sleeve (A36190) from the focusing nut (B16442). Release the special headless screw (A36189) and unscrew the diopter scale (B16443) from the focusing nut. Unscrew the retainer (B16441) from the eyelens cell, thus releasing the field lens (A36184), lens spacer (A36185), and eyelens (A36183) from the eyelens cell. Note the position (for future reference) of the eyelens and the field lens in the eyelens cell and with respect to each other.
    29.	Disassembly of left eyepiece.—Unscrew the eye guard (A36187) from the eyepiece. Unscrew the eyelens cell (A36182) from the focusing nut (B16442). Release the special headless screw (A36189) and unscrew the diopter scale (B16443) from the focusing nut. Scribe a reference line on the threads of the eyepiece sleeve (A36190) and the outside diameter of the reticle cell (A36191). This will serve to locate the reticle cell during assembly. Unscrew the reticle cell from the eyepiece sleeve. Unscrew the eyepiece sleeve from the focusing nut. Unscrew the retainer (B16441) from the eyelens cell, thus releasing the field lens (A36184), the lens spacer
    20
    TM 9-1611
    29-32
    FIELD GLASS, TYPE EE
    (A36185), and the eyelens (A36183). Note the position of the eyelens and the field lens (for future reference) in the eyelens cell with respect to each other. Scribe a reference line on the edge of the reticle cell in prolongation of the graduated line on the reticle (B16444). This line will serve to locate the reticle in the reticle cell on reassembly. Unscrew the retainer (B16445) from the reticle cell, thus releasing the spacer and the reticle.
    30.	Disassembly of body (right or left).— a. Remove the special fillister head screws (A36198), one from each of the four body covers, and remove the body cover.
    5. Inspect each of the Porro prisms for seating and for the location of the headless cone-point adjusting screws (A36195) which serve to hold the Porro prisms in their adjusted positions. The locations of the screw holes in the body can be ascertained from figure 8. The Porro prism toward the objective end of each telescope is held in position by four screws. The Porro prism toward the eyepiece end of each telescope is held by two screws. Porro prisms may be removed in many instances by backing off but one screw. Proper and careful inspection will indicate which screw can be backed off to remove a prism. Remove the plugging cement from the indicated holes on the exterior of the body to render the screwheads available. Loosen the indicated screw or screws, but do not remove unless absolutely necessary.
    c. Remove the special flathead screw (A36199) (one from each of the four prism clips) and remove the prism clip. Remove prism.
    d. After a Porro prism has been released from the body and removed, mark it so that it may be replaced on assembly in the same position and exactly as it was when removed. Repeat the procedure for the other three prisms. Reversing a Porro prism in its seat in the body or assembling a Porro prism in the wrong way may make the final adjustment very difficult because the optical elements cannot be interchanged safely, without affecting the adjustment of the glasses.
    31.	Disassembly of right body from left body.—Remove the clamp screw (A36207), washer (A36212), hinge stop ring (A36210), and the special headless screw (A36204). Remove the screws (A36199 and A36205), the interpupil lary scale (B16451), and the screws (A36204 and A36206). Push or pull the hinge pin (A36203) out (using the screw (A36207), if necessary for gripping) and separate the bodies. Do not lose the washer (A36208). To remove bushing (B16446), withdraw the locking screws (A36196), and unscrew the bushing.
    32.	Removal of stop.—To remove the stop (A36202), withdraw the screw (A36197) (fig. 8, Sec. B-B), and the spring (A36200).
    21
    TM 9-1611
    33-37
    ORDNANCE MAINTENANCE
    33.	Precaution for assembly.—In assembly, parts must be replaced in their original positions. This applies to both mechanical and optical components. Extreme care must be exercised to achieve this objective if final adjustment is not to be unduly complicated.
    34.	Assembly of objectives (right or left).—Apply a thin layer of black navy sealing compound to the seat for the objective lens in the objective cell. Be sure not to apply this sealing compound in excess. Assemble the objective lens with curved face of lens down, away from body, against the shoulder of the cell. Secure the objective in place with the retaining ring.
    35.	Assembly of right eyepiece.—Apply a thin layer of black navy sealing compound to the seat for eyelens in eyelens cell. Assemble the eyelens with the curved surface away from the eye. Insert lens spacer. Assemble field lens to eyelens cell and secure in place with retainer. Assemble diopter scale to focusing nut and secure in place with special headless screw. Apply a thin layer of grease, special, low temperature to the eyepiece sleeve.
    36.	Assembly of left eyepiece.—Assembly of the left eyepiece is identical with the procedure that is followed for assembly of the right eyepiece, except for the last step. Instead of assembling the diaphragm to the eyepiece sleeve, assemble the reticle subassembly. In assembling the reticle subassembly, the etched side of the reticle is down and against the shoulder. The reticle must be exceptionally clean.
    37.	Assembly of body.—Tap the outer surface of the body with a wooden stick to break loose all foreign particles. Clean the interior of the bodies with compressed air. Clean the exteriors with a small amount of solvent, dry-cleaning, and wipe immediately with a dry cloth. Clean the Porro prisms individually immediately prior to replacing them in their seats. Take up the headless cone-point adjusting screws the same amount that they were backed off, in disassembly. Place a thin film of black navy sealing compound around the inside edge of the flanges on the body covers and replace the body covers on the body. Secure with screws. Apply a thin coating of , grease, special, low temperature, to the threads of the objective adapters and screw them into their seats on the body covers.
    Section VI
    CARE AND PRESERVATION
    Paragraph
    Care in handling___________________________________________________________ 38
    Lubrication________________________________________________________________ 39
    Care of optical parts______________________________________________________ 40
    22
    TM 9-1611
    38-40
    FIELD GLASS, TYPE' EE
    38.	Care in handling.—Careless handling and hard knocks seriously affect the field glass. If thrown or dropped on a hard surface, even when cased, the parallelism of the lines of sight may be destroyed by even a slight bending of the frame; rough usage may also scratch or break the lenses, or fracture the dustproof sealing, thus permitting gradual internal fouling and mistiness of vision. Care begins with the case and straps, which should receive the attention due good leather. If a compass is built into the case, clamp it when not in use. The user should determine and memorize not only the interpupiUary setting for his eyes, but that setting at which the glass will slip easily into and out of the case. When placing the field glass in its case, roll the strap on the glass proper neatly about the frame. Make an occasional examination to insure that the shoulder-strap keepers on the case are stitched securely.
    39.	Lubrication.—The field glass may be greased sparingly at long intervals with grease, special, low temperature, furnished by the Ordnance Department for fire-control instruments. The only parts requiring lubricants are the eyepiece threads and the hinge.
    40.	Care of optical parts.—a. To obtain satisfactory vision, it is necessary to keep the exposed surfaces of the lenses and other parts clean and dry. Corrosion and etching of the glass surface can thus be prevented or retarded.
    ~b. Do not wipe lenses with the fingers. When the field glass is in use, wipe the lenses frequently with clean lens tissue paper. No substitute should ever be used for this purpose.
    c. Moisture due to condensation may collect on the optical parts when the temperature of the instrument is below that of the surrounding air. this may be removed by placing the instrument in a warm place. Heat from strongly concentrated sources should never be applied directly as it may cause unequal expansion of parts with resulting inaccuracies in observation.
    cl. For dusting optica] parts, use only a clean camel’s-hair brush. To remove dust, brush the glass lightly and rap the brush against a hard body to knock out dust particles.
    e. To remove oil or grease from optical surfaces, apply ethyl alcohol, sparingly, with a clean camel’s-hair brush and rub gently with clean lens paper. If alcohol is not available, breathe on the glass and wipe clean. Repeat this operation several times until clean.
    /. Use of polishing liquids or pastes for polishing lens is forbidden.
    g. W hen optical assemblies are removed, wash the exposed surfaces in ethyl alcohol, then wrap the assemblies in clean lens tissue pending reassembly.
    23
    ORDNANCE MAINTENANCE
    TM 9-1611
    Appendix LIST OF REFERENCES
    1.	Standard Nomenclature Lists.
    a.	Cleaning, preserving, and lubricating materials_SNL K-l
    b.	Fire control instruments.
    Binocular, M-3__________________________________SNL F-210
    Glasses, field, type EE, 6 power________________SNL F-34
    Glass, field, type EE, 6 power__________________'
    Glass, field, type EE, 6 power (U. S. naval gun g^L p 14g factory), and_________________________________[
    Glass, field, Huet type, 8 power________________
    Sighting and fire control equipment_____________ SNL F-l
    c.	Kit, repair, optical, for field artillery________ SNL F-21
    d.	Current Standard Nomenclature Lists are as tab-
    ulated here. An up-to-date list of SNL’s is maintained as the “Ordnance Publications for
    Supply Index”_________________________________OPSI
    2.	Explanatory publications.
    a. Cleaning, preserving, and lubricating materials-_ TM 9-850 b. Fire control instruments.
    Field artillery fire control instruments________TM 6-220
    Instruction guide, the instrument repairman_____TM 9-2602
    c. Inspection and repair.
    Inspection of leather and leather equipment_____TM 10-226
    Material inspection and repair__________________TM 9-1100
    d. Maintenance.
    Lubrication instructions, general, fire control instruments___________________________________OFSB 6-F-l
    Maintenance of material in hands of using troops- OFSB 4—1
    Special instructions, group F material__________OFSB 4-8
    [A. G. 062.11 (2-19-42).]
    By order of the Secretary of War :
    G. C. MARSHALL, Official:	Chief of Staff.
    J. A. ULIO,
    Major General, The Adjutant General. Distribution :
    IBn 9 (1) ; IC 9 (3).
    (For explanation of symbols see FM 21-6.)
    24
    U. S. GOVERNMENT PRINTING OFFICE: 1942
    For sale by the Superintendent of Documents
    Washington. D. C.
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    UNT LIBRARIES DENTON TX 78203
    1001895652