MIL-PRF-49367C (CR)
3.5
Performance characteristics.
3.5.1 Equivalent focal length. The equivalent focal length of the
objective lens shall be 155 mm, ±1 mm.
3.5.2 Flange focal distance.
The flange focal distance shall be
1.20 mm, ±0.50 mm.
3.5.3 T-number. The T-number of the objective lens shall not be
greater than T/1.70 measured with a S-20 extended red (ER) photomultiplier
tube and a 2854, ±200 Kelvin (K) light source.
3.5.4 Veiling glare/stray light. The veiling glare/stray light
luminance contribution shall not be greater than 2.5 percent of total
illumination when viewing a black spot subtending 1° in the field of view
centered in a uniformly illuminated 180° field.
3.5.5 Linear distortion. The linear distortion of the objective shall
be less than 2 percent pincushion at the edge of the 25mm format.
3.5.6 Field of view. The field of view of the objective shall be a
minimum of 156 milliradians when measured across a 25mm format.
3.5.7 Relative illumination. The relative illumination of the image
formed by the objective shall not vary across the 25mm format by more than
±80 percent of maximum value.
3.5.8
Modulation transfer function.
3.5.8.1
The modulation transfer function (MTF) shall meet the
requirements of Figures 1 and 2 when measured on-axis and off-axis (2/3 field)
all in the same focal plane. The measurement shall be made over the spectral
band as defined by the S-20 Extended Red Response Curve.
3.5.8.2
Alternate method for verification of MTF. The MTF requirement
for the objective may be verified by attaching the objective to the battery
housing assembly, eyepiece assembly and image intensifier assembly to assemble
a sight per MIL-PRF-49064E. Verification of the requirements of paragraph
3.6.3, Resolution, of MIL-PRF-49064E at the sight level shall verify the MTF
requirement of the objective.
3.5.9 Reticle movement. Two external control knobs shall control the
position of the reticle pattern viewed by the observer using the sight. One
control shall move the reticle pattern in azimuth; another control shall move
the reticle pattern in elevation. An adjustment made by turning one control
shall not cause the reticle to deviate from a straight line of travel by more
than 0.5 milliradian. Adjustment will be apparent to the operator by tactile
indexing with audible clicks.
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