MIL-DTL-62478C(AT)
3.2.3 Nonmetals. All nonmetals shall be suitable for their intended purpose during the
normal life and under the environmental conditions specified. Use of elastomerics shall be
governed by the age controls of SAE AS1933 (see 4.5).
3.2.4 Protective window. The optical coupler objective lens shall be covered by a
protective window with a protection level equivalent to BK 7 glass or better (see 4.5 and 6.3).
3.2.5 Purge and charge. The optical coupler shall be purged of all the air and the
moisture, and charged to an internal pressure of 0 ± 0.2 pounds per square inch gage (psig)
(0 ± 1.38 kilopascals (kPa)) with dry nitrogen conforming to A-A-59503, Type I, Class 1, Grade
A or B (see 4.5).
3.3 Operating requirements. Each optical coupler shall provide the following functional,
operational, and performance capabilities.
3.3.1 Resolution. Resolution specified in 3.3.1.1 and 3.3.1.2 shall be for a high contrast
target which shall be the USAF 1951 test chart or the NBS 1010A microcopy test chart
(see 4.6.1).
3.3.1.1 Optical coupler resolution. The optical coupler shall clearly resolve an angle of
104 arc seconds, or less, on axis (see 4.6.1.1).
3.3.1.2 Integrated system resolution. When the optical coupler is assembled between the
G/VLLD and the ITA, the system shall clearly resolve an angle of 8 arc seconds or less, on axis,
with the observer s eye anywhere within the exit pupil of the ITA eyepiece. The integrated
system shall also clearly resolve the G/VLLD LED data numbers which are approximately in the
plane of the G/VLLD reticle (see 4.6.1.2).
3.3.2 Astigmatism. The optical coupler axial astigmatism shall not be greater than
0.2 diopter (see 4.6.2).
3.3.3 Magnification. The optical coupler shall provide a magnification of 1 ±7% from
the optical coupler input to the ITA output (see 4.6.3).
3.3.4 Entrance pupil. The optical coupler shall provide an entrance pupil that shall not
reduce the integrated system exit pupil to less than 0.22 inch (in.) (5.5 millimeters (mm)) when
the integrated system is properly pupil matched (see 4.6.4).
3.3.5 Field of view. The integrated system, when incorporating the optical coupler, shall
provide a real field of view that is not less than 5 degrees (0.087 radians) in any pupil matched
condition (see 4.6.5).
3.3.6 Lateral color. The optical coupler shall provide that the lateral color of the system
shall not be greater than 3 minutes of an arc out of the system for wavelengths between
0.0000192 in. (486 nanometers (nm)) and 0.0000258 in. (656 nm) (see 4.6.6).
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