MIL-DTL-62420B(AT)
b. Calculations.
(1)
Transmission (T) at each wavelength is:
T = Radiance with the periscope in the optical train
Radiance without periscope in optical train
(2)
The optical density (O.D.) is:
O.D. = log (1/T)
4.7.1.6 Angular deviation. The applicable drawing, the periscope shall be mounted
vertically and shall be viewed through the exit window with an observation telescope placed
normal to the exit window and equipped with a centercross-hair reticule. Horizontal lines on a
wall chart shall be viewed representing the upper and lower angular deviation limits. The
observed cross hair must fall between the upper and lower deviation limits. Alternate method (1):
a light collimator can be used in place of the wall chart. Alternate method (2): a hene laser can
be used in place of the observation telescope.
4.7.2 Cleaning spray.
4.7.2.1 Vehicle exterior cleaning spray. The portion of the assembly above the sealing
surface shall be exposed to a water jet or stream spray using high grade commercial cleaning
agents that meet the environmental and performance requirements of this specification. The jet
shall be applied perpendicular to and at a distance no closer than one ft (30.5 centimeter (cm)) nor
farther than 2 ft (61 cm) from the component surface at a cleaning rate of 1 square foot per
minute (ft2/min) (0.093 square meter per minute (m2/min)) for a period of 10 minutes. The water
jet shall be derived from a nozzle having an orifice diameter of 0.25 in. (0.6 cm) and a nozzle
pressure of 110 pounds per square inch gage (psig) (758 kPa). Immediately following the
cleaning, the periscope shall be subjected to a cold water rinse air dried and subsequently shall be
subjected to and pass the performance tests of 3.4.1.
4.7.2.2 Vehicle interior cleaning spray. The portion of the assembly below the sealing
surface shall be exposed to a jet spray of tap water applied perpendicular to and at a distance no
closer than one foot nor farther than 2 ft from the component surface at a cleaning rate of
1 ft2/min for a period of 10 minutes. The water jet shall be derived from a nozzle having an
orifice diameter of 0.25 in. and a nozzle pressure of not more than 25 psig (172 kPa). After the
periscope has been air dried, the assembly shall be subjected to and pass the performance tests of
3.4.1.
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