MIL-PRF-49173B(CR)
4.4.1 Test conditions. Each imager shall be inspected at ambient temperature (see 6.5.2).
Tests shall be conducted with blackbody/graybody radiation over the 7.6 to 11.75 micrometer
region using the configuration shown in Figure 2. The test collimator used shall have a
wavefront error of less than 4.0 wavelengths (peak-to-peak) at 632.8 manometers (Ref) over the
clear circular aperture of the unit under test. Linearity of radiometric measurement setups shall
be within 5 percent.
4.5 Methods of inspection. The contractor/supplier may use his own test methods,
measuring devices, tools, fixtures and other equipment during the conduct of verification testing.
This specification cites no specific testing procedure as long as all the performance requirements
per Section 3 are fully verified as being met.
4.5.1 Effective Focal Length (EFL). Measure compliance with 3.5.1. Recommend using
procedures found in 6.3. Failure to meet the requirement shall constitute failure of the sample.
4.5.2 f/number. Measure compliance with 3.5.2. Recommend using procedures found in
6.3. Failure to meet the requirement shall constitute failure of the sample.
4.5.3 Linear distortion. Measure compliance with 3.5.3. Recommend using procedures
found in 6.3. Failure to meet the requirement shall constitute failure of the sample.
4.5.4 Modulation transfer function (MTF). The MTF shall be measured either
continuously or in eight (8) discrete steps from 0 to 16 cycles per millimeter (cy/mm). The MTF
test shall be run at infinite conjugates. On-axis MTF shall be measured and shall not be less than
the MTF in Figure 1. Off-axis radial MTF shall be measured in the same plane used for the on-
axis image parallel to the plane defined by the datum A of Figure 2. The off-axis MTF shall be
measured at two (2) points in the field 90 degrees apart. Failure to meet the requirement (3.5.4)
shall constitute failure of the sample.
4.5.5 Relative Illumination (RI). RI shall be measured in two (2) mutually perpendicular
planes with the first plane measured across the greatest distance of the oval shape of the mirror.
Failure to meet the requirement (3.5.5) shall constitute failure of the sample.
4.5.6 Flange focal distance (FD). FD shall be measured from datum A in Figure 2 to the
flat field plane of the best MTF. Failure to meet the requirement (3.5.6) shall constitute failure of
the sample.
4.5.7 Field of view (FOV). Measure FOV as part of the relative illumination requirement
of 4.5.5. Failure to meet the requirement (3.5.7) shall constitute failure of the sample.
4.5.8 Optical transmittance. Measure optical transmittance. Failure to meet the
requirement (3.5.8) shall constitute failure of the sample.
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