ARMY TM 5-6675-308-34
MARINE CORPS TM 08837A-34/2
c. Adjustment. There are three adjusting screws on
Test. To test the optical plumb, suspend the
b.
plumb bob from the leveled instrument and
the telescope, a horizontal screw on the left side
mark a point on the ground exactly under the
and two slant screws on the right side. If the
point of the plumb bob. Remove the plumb bob
vertical line does not continuously bisect the
from the instrument and check to insure that the
sighted point, turn the two slant screws an equal
instrument is accurately leveled (i.e., the vertical
amount in opposite directions to rotate the reti-
axis is truly vertical). Look into the eyepiece of
cle until the vertical crossline does bisect the
the optical plumb. If it is in correct adjustment,
point throughout the elevation and depression of
the mark on the ground will be centered in the
the telescope.
reticle.
c. Adjustment. If the point on the ground is not
centered in the optical plumb reticle, center the
a. Purpose. The purpose of the horizontal collima-
point by means of the three capstan adjusting
tion adjusting is to make the line of sight
screws located near the optical plumb eyepiece.
perpendicular to the horizontal axis of the tele-
Two of these adjusting screws are located on
scope.
opposite sides of the eyepiece, and the third
b. Test. To test the horizontal collimation, select a
adjusting screw is located below the eyepiece
well-defined point at least 100 meters from the
opposite a sprint-loaded plunger. The bottom
instrument and at approximately the same rela-
adjusting screw is locked in place by a capstan
tive height. With the telescope in the direct
retaining nut, which is located immediately
position, center the vertical crossline on the
above the head of the adjusting screw. With an
selected point. Set the horizontal circle to any
adjusting pin, loosen the retaining nut and raise
reading less than 3,200 mils, close the cover on
or lower the reticle by turning the bottom ad-
the circle-setting knob, and record the reading.
justing screw to move the reticle image along
Plunge the telescope to the reverse position and
the axis of the optical plumb in the same direc-
take a second reading on the same point. The
tion that the screw travels. The two side adjust-
instrument operator should repeat both readings
ing screws are used to move the image of the
to insure that no error was made in reading the
reticle in the opposite direction from their
instrument. These two readings should differ by
travel. If it is necessary to use these screws, they
3,200 mils. Assuming no error in the pointings or
should be rotated an equal amount in opposite
readings, any discrepancy between actual differ-
directions, It is usually necessary to loosen the
ence in the two readings and 3,200 mils is the
screw below the eyepiece slightly to adjust the
apparent error, or twice the horizontal collima-
screws on the side and vice versa. To make the
tion error. If this discrepancy exceeds plus or
adjustment, loosen one of the two opposed
minus 0.100 mil (20"), the horizontal collimation
screws and the retaining nut slightly. The spring-
adjustment should be performed.
opposed adjusting screw should be used for nec-
essary adjustments, and the opposed adjusting
c. Adjustment. For the purpose of illustration as-
screws should be used to complete these adjust-
sume that the horizontal circle reading in the
ments. When the adjustment is complete, the
direct position is 0000.200 mil and in the reverse
two opposed adjusting screws must be faily tight.
position is 3,200.800 mils. With the telescope in
Lock the bottom adjusting screw in place by
the direct position, use the coincidence knob to
tightening the retaining nut.
set the mean value (0.500) on the micrometer
scale. Using the horizontal tangent screw, bring
the main scale into coincidence with a value of 0
mil on the scale. In doing this, the vertical
crossline is moved off the point by the amount of
a. Purpose. The purpose of the verticality adjust-
the horizontal collimation error. The vertical
ment is to make the vertical crossline of the
crossline is then aligned on the selected point by
reticle lie in a plane perpendicular to the hori-
lateral movement of the reticle within the tele-
zontal axis of the telescope.
scope. To move the reticle, loosen (tighten) the
b. Test. To test the verticality of the vertical
two adjusting screws in the slant position on the
crossline, select a well-defined distant point as
right side of the telescope equally, and tighten
near as possible to the horizontal plane of the
(loosen) the single adiusting screw on the left
instrument and center the vertical crossline on
side of the telescope. For moving the reticle, the
the selected point. With the vertical tangent
adjusting screw(s) should be loosened before the
screw, elevate and depress the telescope. If the
screw(s) on the opposite side of the telescope is
vertical crossline continuously bisects the point,
tightened. Repeat the test and adjustment proce-
the adjustment is correct.
dure until the difference between the direct and
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