MIL-PRF-38169A
b.
Additional tests for class 3 lenses
(6)
Extended electromagnetic radiation transmittance (see 4.4.7)
(7)
Colorfastness to light (see 4.4.12)
(8)
Resistance to thermal shock (see 4.4.13)
(9)
Durability of coatings (see 4.4.14)
4.4
Tests.
4.4.1 Examination of product. Each visor or goggle lens shall be visually examined to
determine conformance to this specification with respect to materials; design and construction;
peeling, warping, cracking, crazing, optical distortion of the critical areas, or any other optical
defects during testing; and interchangeability.
4.4.2 Prismatic deviation. A telescope, lensometer, projection lantern, or any other suitable
instrument shall be used to test the prismatic deviation. The instrument shall include a target
which can be brought into sharp focus, as observed through an eyepiece or projected upon a
screen, and an aperture not over 1 centimeter in diameter fixed at a definite position along the axis
of the optical system. The design of the instrument shall be such that the refractive power in the
principal meridian of the visor placed across the test aperture can be determined to within 0.03
diopter. Vertical and horizontal prismatic deviations shall apply to readings taken on the visor as
worn, that is, the distance of 1.70 inches from the concave surface of the visor when instruments
other than the lensometer are used. All measurements shall be made in areas delineated in the end
item specification, drawing, or as specified by the procurement activity (see 6.2.f).
4.4.2.1 Vertical prismatic deviation. Base up prism shall be designated positive (+) and base
down prism shall be designated negative (-). The vertical prismatic deviation is calculated by
determining the algebraic difference between point C for the right eye and point C for the left eye.
4.4.2.2 Horizontal prismatic deviation. Base out prismatic deviation shall be designated positive
(+) and base in prismatic deviations shall be designated negative (-). The horizontal prismatic
deviation shall be calculated by determining both the algebraic sum and difference between point
C for the right eye and point C for the left eye.
4.4.3 Refractive power. The refractive power shall be determined with the same apparatus used
for measuring prismatic deviation (see 4.4.2 and 6.3.5).
4.4.4 Luminous transmittance. The luminous transmittance of the critical and non-critical areas
(see figure 1) of class 1, class 2, and class 3 visor or goggle lenses shall be determined using an
acceptable commercial process such as that contained in ASTM D 1003 (see 6.3.2.1).
7
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