MIL-PRF-49368C (CR)
3.6
Performance characteristics.
3.6.1 Effective focal length.
The effective focal length shall be
26.5, ± 0.3mm.
3.6.2 Flange focal distance. The flange focal distance of the eyepiece
assembly at zero diopter shall be 4.753 ± 0.207, -0.435mm.
3.6.3 Field curvature. The field curvature of the eyepiece assembly
shall deviate no more than ±1/4 diopter over the full 25mm flat format.
3.6.4 Linear distortion. The linear distortion of the eyepiece
assembly shall be between 0 and 9 percent pincushion distortion at the edge of
the 25mm format.
3.6.5 Exit pupil. The exit pupil diameter shall be 5.0, ± 0.2mm at eye
relief of 28.0, ± 0.5mm.
3.6.6 Transmission. The transmission of the eyepiece assembly shall be
not less than 80 percent over the full eyepiece assembly aperture for the
spectral output of the P-20 phosphor.
3.6.7 Resolution. The eyepiece shall have an on-axis resolution of not
less than 50 lp/mm. The resolution measurement shall be made using a 2856K
light source filtered to simulate the phosphor.
3.6.8 Diopter adjustment. The diopter adjustment shall operate
smoothly, without binding, throughout its complete range of movement at all
operating temperatures specified herein. Dynamic torque shall be between 2
and 20 inch-pounds.
3.6.9 Diopter range. The eyepiece assembly focus range shall not be
less than 8 diopters when one rotational stop is set at -6 (+1/4 -0) diopters.
3.7
Environmental.
NOTE: Post-environmental verification of performance shall be Exit pupil
(3.6.5), Transmission (3.6.6) and Resolution (3.6.7). Failure to meet these
requirements shall constitute failure due to degradation of performance of
input or output characteristics per the damage technical interpretation of
3.10.1.
3.7.1 Temperature Extremes. The eyepiece assembly shall not be damaged
(see 3.10.1) after storage in any temperature from -51°C to +68°C. The
eyepiece assembly shall not be damaged (see 3.10.1) after being subjected to
repetitive temperature changes between +23°C and +68°C in 5 minutes and
between +23°C and -51°C in 5 minutes. The transition from +68°C to -51°C and
from -51°C to +68°C shall include a 2 hour soak at +23°C. Soak time at
temperature extremes shall be sufficient for the entire eyepiece assembly to
attain stabilization.
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