(2) These cleaners evaporate quickly and
d. Leather, To clean leather, scrape off ac-
have a drying effect on the skin. If used without
cumulations of grease and dirt with wooden
gloves, they may cause cracks in the skin and, in
instrument. Clean with leather dressing; or wash
the case of some individuals, mild irritation or
with saddle soap and water, rinsing lightly and
applying neat's foot oil while still damp. Allow
(3) Avoid getting petroleum products, such
water-soaked items to dry in shade before com-
as dry-cleaning solvent or mineral spirits paint
mencing above process. Do not dry in direct sun
or by an artificial heat source.
parts, as they will cause the rubber to deteriorate.
e. Canvas, To clean canvas, scrub with a clean
(4) The use of diesel fuel oil, gasoline, or
dry brush or with brush and water. To remove
benzene (benzol) for cleaning is prohibited.
grease and oil, scrub with saddle soap. Rinse and
dry thoroughly for 24 hours. Spray or brush with
3-12. Preventive-Maintenance Services.
approved waterproofing compound.
a. Purpose. To insure efficient operation, it is
f. Optical Surfaces.
necessary that the observation telescope be syste-
(1) To remove dust, lint, or other foreign
matically inspected at intervals each day it is
matter from lenses and windows, brush the glass
operated, and weekly, so that defects may be
lightly with a clean artist's camel's-hair brush.
discovered and corrected before they result in
Rap the brush against a hard body to knock out
serious damage or failure. Certain scheduled
the small particles. Repeat this operation until
maintenance services will be performed at these
all dust is removed.
designated intervals. Any defect or unsatisfac-
tory operating characteristics beyond the scope
(2) To remove oil or grease from optical
of the operator or organizational mechanic to
surfaces when the temperature is above S2F.,
correct must be reported at the earliest oppor-
breathe heavily on the glass and wipe off with
tunity to the supporting ordnance unit for
clean lens tissue paper. Repeat this operation
(3) In cold weather, below 32 F., optical
b. Condition of Optics. Looking through the
surfaces should be cleaned with lens tissue paper
eyepiece and objective ends of the telescope, there
moistened with alcohol. If alcohol is not available
will be no objectionable dirt, smears, scratches,
use dry lens tissue paper. Alcohol should never
digs, condensate, fungus growth, chips, fractures,
be applied directly to the lens surfaces, as any
or cement separation. The "shading or shadow-
excess may injure the sealing compound, Do not
ing" technique will be used to determine the
breathe on the glass, since this would ice the
presence of objection condensate or smears.
"Shadowing" is the technique of looking into the
eyepiece or objective end of the sight obliquely
on the optical elements of the instrument when
face in the optical system. With this method; the
the temperature of the parts is lower than that
surfaces of the internal optical elements are drab
of the surrounding air. This moisture, if not ex-
gray in appearance and all defects (condensate,
cessive, can be removed by placing the instrument
scratches, etc. ) show up as white particles.
in a warm place. Heat from extreme concentrated
sources should not be applied directly, as it may
Note. Rejection is to be based upon only those defects
cause unequal expansion of parts, thereby result-
that are apparent when the telescope is used in a manner
simulating field conditions. The telescope will not be re-
ing in damage to parts and inaccuracies of
jected for defects that can be detected only by the shading
or shadowing technique.
g. General Precaution in Cleaning.
c. Services. Operator's and organizational
mechanic's preventive-maintenance services are
(1) Dry-cleaning solvent or mineral spirits
paint thinner are inflammable and should not be
with the observation telescope M49 must thor-
used near an open flame. Fire extinguishers
oughly train its personnel in performing the
should be provided when these materials are used,
maintenance procedures for this materiel.
Use only in well-ventilated places.