MIL-DTL-62420B(AT)
4.6.1 Verification alternatives. The manufacturer may propose alternative test methods,
techniques, or equipment, including the application of statistical process control, tool control, or
cost effective sampling procedures to verify performance. See the contract for alternatives that
replace verification methods required by this specification.
4.7 Operating requirement verification.
4.7.1 Optical characteristics. The test to determine compliance with mirror and window
laminations, lint, bubbles and inclusions shall be made by viewing the periscope through the exit,
or entrance, window against a uniformly illuminated translucent ground glass field (or equivalent)
having a brightness of approximately 300 foot candles.
4.7.1.1 Resolution. The resolution shall be performed utilizing a holding medium to
support the periscope during the test, a diopter with a magnification of at least three power (3x)
and a resolving power chart. The resolving power chart shall represent the angular subtense for
the seconds of arc specified in 3.4.1.1, and shall contain four line sets as shown in figure 1. The
chart of appropriate dimensions may be located in a collimator or it may be viewed directly. The
diopter's eyepiece shall be focused to its reticle to accommodate the individual inspector's eye.
Using the diopter, the target shall be resolved in each of the four meridians, and the diopter for
each meridian shall be recorded. This operation shall be repeated in nine regions of the clear
aperture, three readings approximately 1.5 in. (38 mm) from each end and three readings in the
center. The total spread of the four readings obtained in each of the nine areas shall not exceed
0.25 diopter.
4.7.1.2 Spherical power. The average of the horizontal and vertical target focus readings
obtained in each of the nine areas, as outlined in 4.7.1.1, shall be in accordance with the spherical
power requirement of 3.4.1.2.
4.7.1.3 Astigmatism. The algebraic difference in focus between the horizontal and
vertical target focus readings obtained in each of the nine areas, as outlined in 4.7.1.1, shall be in
accordance with the astigmatism requirement of 3.4.1.3.
4.7.1.4 Photopic transmission (PT) measurement. The periscope shall be measured at
0 +2 degrees incidence and shall be tested in accordance with the following:
a. Apparatus. One of the following systems shall be utilized:
(1)
A constant current tungsten lamp
A monochromator
A detector
(2)
A double beam spectrophotometer
(3)
A Pritchard type photometer
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