MIL-DTL-11352K(AT)
4.6.3.2 Optical density. To determine conformance to 3.4.2, all vision blocks with laser
filters shall be tested using the apparatus specified in 4.6.3.1. The optical density of each laser
protected vision block shall be measured along the optical axis. Optical density shall be
measured along the optical axis at wavelengths of 694 nm and 1064 nm. The measurement
system shall be traceable to the National Institute of Standards and Technology (NIST) through a
calibrated absorption type neutral density filter for nominal optical densities of 3 and 4. The
measurement system shall be capable of measuring the NIST traceable filters to an accuracy of
±0.1 optical density (O.D).
a. Calculations.
(1) Transmission (T) at each wavelength is:
Radiance with vision block in the optical train
T=
Radiance without vision block in optical train
(2) The O.D. is defined as:
O.D. = log (1/T)
4.6.3.3 Resolving power. To determine conformance to 3.4.3, a resolution test shall be
standard and shall be performed using one of the resolving power charts (see figure 5). An
auxiliary telescope is used to obtain sufficient magnification. A resolving power chart shall
consist of four sets of lines, all sets either entirely three or entirely four lines at 45 degree steps
(horizontal, vertical, and two at 45 degrees). The three line sets shall contain lines that are five
times as long as they are wide. The four line sets shall contain lines that are seven times as long
as they are wide. The widths of lines and spaces shall be equal. The lines may be either black
on a white background, or white on a black background. There shall be an identifying numeral
in the center of the four sets of lines. The contrast shall be 100:1 minimum. The chart of
appropriate dimensions may be located in a collimator, or it may be viewed directly. In the latter
case, the chart shall be at least 2 M2 feet from the telescope objective, where M is the power of
the vision block being tested. The angular subtense of a chart is measured in seconds and equals
arc tangent 2W/X, where W is the width of a chart line and X is either collimator focal length or
distance from chart to vision block under test. The vision block under test is aligned so the chart
is in the center of the field. The auxiliary telescope is added and oriented to again center the
chart. With the diopter scale of the auxiliary telescope at zero, the vision block under test shall
be focused on the numeral in the resolving power target. In reading resolution, the auxiliary
telescope may be focused plus (+) or minus (-) 1/8 diopter for each of the four meridians. All
four test meridians shall have the correct line count. The limit of resolution is reached when
individual lines within the pattern are no longer clearly separated.
4.6.3.4 Ballistic resistance. To determine conformance to 3.4.4, eight of each type, class,
duty, and part number vision blocks shall be forwarded to a place designated by the Government
for testing. Testing shall be conducted in accordance with applicable provisions of Appendix A
to this specification (see 6.2, 6.5.2 and A4.2.6).
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