MIL-PRF-49366C(CR)
3.5
Performance characteristics.
3.5.1 Effective focal length.
The effective focal length of the
objective shall be 95mm, ± lmm.
3.5.2 Flange focal distance.
The flange focal distance shall be
1.20mm, ± 0.50mm.
3.5.3 T-number. The T-number of the objective shall not be greater
than T/1.70 measured with an 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 253 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 (MTF).
3.5.8.1 Modulation transfer function. The modulation transfer function
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 define by the S-20 Extended Red (ER) Response
Curve.
3.5.8.2 Alternate method for verification of MTF. The MTF requirement
for the objective can be verified by attaching the objective to the battery
housing assembly, eyepiece assembly and image intensifier to assemble a sight
per MIL-PRF-49063. Verification of the requirements of paragraph 3.6.3,
Resolution, of MIL-PRF-49063 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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