MIL-DTL-43511D
3.4 Areas of vision. Unless otherwise specified, the visor shall have three areas of vision which
are identified as: outside the area of vision (no optical requirement), non-critical area of vision,
and critical area of vision. The center point for the right and left optics shall be identified as
point "C". The location of point "C" and the location and size of the three areas of the visor
identified above shall be as specified in the end item specification, drawing, or contract as
applicable. The critical area is approximately a 50 degree radius field of view from the primary
line of sight intercept point on the visor for the designed right and left eye locations. The areas
within 1 mm (1/16") of the edges of the visor are non-critical areas. Regions that rest against the
helmet shell are outside the area of vision. Figure 1 shows a typical layout of a visor and is
intended to serve as a guide only for use by Government agencies to develop their detailed
requirements. Unless otherwise specified in the end item specification, drawing, or contract as
applicable, the numbered circles within the critical areas are designated as points of choice for
prismatic and distortion tests. Points bearing the same number, for example 5R and 5L, shall be
compared with each other, except points 2R and 2L (outermost points on left and right sides of
visor) shall be compared with point 3 (center point of visor) when measuring refractive power or
prismatic deviations.
3.5 Performance.
3.5.1 Prismatic deviation. Prismatic deviation stated herein includes the inherent prismatic
power resulting from nonparallel surfaces of the material and dissimilar curvature between the
critical areas. The vertical and horizontal prismatic deviations shall be tested as specified in
4.3.5.
3.5.1.1 Vertical prismatic deviation. The vertical prismatic deviation through point "C" for the
left and right eyes shall be no more than 0.18 prism diopters. The vertical prism along any
individual line of sight through the critical area shall not exceed 0.25 prism diopters.
3.5.1.2 Horizontal prismatic deviation. The horizontal prismatic deviation through point "C" for
the left and right eyes shall be no more than 0.18 prism diopters BASE IN and no more than 0.25
diopters BASE OUT. The horizontal prism along any individual line of sight through the critical
area shall not exceed 0.25 prism diopters.
3.5.2 Refractive power. The refractive power shall not exceed plus or minus 0.125 diopters at
point "C" and at all other points of choice for the left and right optics, when tested as specified in
4.3.5.
3.5.3 Luminous transmittance (see 6.5)
3.5.3.1 Class 1 visor. The luminous transmittance of class 1 visor shall be not less than 85
percent throughout the critical area when tested as specified in 4.3.5.
3.5.3.2 Class 2 visor. The luminous transmittance of class 2 visor shall be within 12 to 18
percent when measured at point "C", left and right optics. The total visible transmittance of the
visor shall not vary more than 3.0 percentage points. Tests shall be as specified in 4.3.5.
3.5.4 Optical density.
3.5.4.1 Class 3 visor. The optical density (OD) of the class 3 visor shall be between 0.83 and
0.60 OD when measured at point "C" left and right optics. The OD at any point in a horizontal
meridian of a given visor shall not vary by more than 0.1 OD from other points on the same
meridian. The class 3 visor shall consist of a class 1 visor with a gradient tint, darker at the top,
conforming to an OD gradient of 0.4 OD/inch + 0.06 OD when measured at point "C" to a
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