MIL-PRF-49148D(CR)
3.5.3 Linear distortion. The objective lens shall have between 9 percent
and 12 percent barrel distortion.
3.5.4 Modulation Transfer Function (MTF) on axis. The MTF shall be not
less than the values specified in Table I when tested on axis with a sine wave
pattern setup that utilizes an S-20-ER response photomultiplier and a tungsten
illumination source operated at 2854K ±200K color temperature. The test shall
be repeated with the objective rotated 90 degrees about the optical axis.
TABLE I. Objective lens modulation transfer function.
+----------------------------------------------------------------------------+
¦ Test Frequency
¦
Modulation Transfer
¦
¦ (cycles/millimeter)
¦
(Percent)
¦
¦ on the Image Intensifier
¦
¦
+-----------------------------------------+----------------------------------¦
¦
10
¦
84
¦
¦
20
¦
70
¦
¦
30
¦
55
¦
¦
40
¦
40
¦
+----------------------------------------------------------------------------+
3.5.5 T-number. The T-number shall be no greater than 1.25 when tested
using a light source operated at 2854K ±200K color temperature and a photo-
detector with an S-20ER response.
3.5.6 Veiling glare. The veiling glare (stray light) shall be no
greater than 2.5 percent when using a photodetector with an S-20ER response.
3.5.7 Flange focal length. The flange focal length shall be not less
than 0.039 inches (0.99lmm) when measured from the outermost flange surface of
the 1.5-inch diameter central area of the lens retainer.
3.6 Environmental. Verification of conformance after environmental
tests shall be Modulation transfer function (3.5.4), Veiling glare (3.5.6) and
Flange focal length (3.5.7).
3.6.1 Temperature Extremes. The objective lens shall not be damaged
nor suffer degradation of performance (see 3.10.1 and 3.10.4) after being
subjected to storage at +68°C to -51°C. The objective lens shall not be
damaged nor suffer degradation of performance (see 3.10.1 and 3.10.4) 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. Soak time at each
temperature extreme shall be sufficient for the objective lens to attain
temperature 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
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