MIL-PRF-49157B
3.4.3 Linear distortion. The linear distortion of the objective lens
assembly at the edge of the 18 mm format shall be between 2.5 percent and 8.5
percent barrel distortion.
3.4.4 Field of view.
The field of view of the objective lens assembly
shall be 40o +1/-3.
3.4.5 F/number.
The F/number of the objective lens assembly shall be no
greater than F/1.1.
3.4.6 T/number.
The T/number of the objective lens assembly shall be no
greater than T/1.25.
3.4.7 Stray light. The stray light of the objective lens assembly shall
be no greater than 2.5 percent.
3.4.8 Modulation transfer function (MTF). The MTF values of the objective
lens assembly shall not be less than those specified in Table I.
Table I.
Modulation transfer function.
Spatial Frequency1
Orientation
10 lp/mm
20 lp/mm
30 lp/mm
40 lp/mm
on-axis
76%
62%
50%
40%
14° off-axis
radial2
60%
12%
0%
0%
14° off-axis
tangential2
60%
12%
0%
0%
1
in units of
line pairs per millimeter (lp/mm)
2
unrefocused
from on-axis measurement
3.4.9 Field flatness/field tilt. The field flatness/field tilt of the
objective lens assembly shall be within 0.3 mm across the entire 18 mm format for
radial and/or tangential focus.
3.4.10 Relative illumination. At full aperture, the image illuminance at
the edge of the format shall be no less than 30 percent of the image illuminance
on axis.
3.4.11 Weight. The weight of the objective lens assembly, without the
protective cap (see drawing A3144484), shall not exceed 104 grams.
3.5
Environmental characteristics.
3.5.1 Temperature extremes. The objective lens assembly shall not be
damaged (see 3.9.1) by storage in any temperature from +23oC to +68oC or from
+23oC to -51oC. The objective lens assembly shall not be damaged (see 3.9.1)
after being subjected to repetitive temperature changes between +23oC to +65oC in
a 5 minute period and between +23oC to -51oC in a 5 minute period. Soak time at
temperature extremes shall be sufficient for the entire objective lens assembly
to attain stabilization. Time for temperature stabilization is defined as the
amount of time required for the most internal part of the unit under test to
achieve the specified temperature.
3.5.2 Humidity. The objective lens assembly shall not be damaged (see
3.9.1) when subjected to an atmosphere with a relative humidity of 95 percent ± 5
over a temperature range of 20oC to 65oC.
3
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