MIL-DTL-48554B
3.5.2 Counter box. The counter box of the telescope shall be capable of sustaining
an internal pressure of 5.0 + 0.1 psig for a minimum of one hour with no evidence of
leakage.
3.5.3 Purging. The optical assembly and counter box of the telescope shall be
purged with dry nitrogen supplied at a pressure of 8.00 + 0.25 psig until the dew point of
the emergent gas is no higher than -25 °F. Purging apparatus shall be removed when relief
valve is reseated and maintains a minimum pressure of 5 psig.
3.6 Cleanliness.
3.6.1 Dirt. The maximum length and/or width of any particle appearing on the
reticle surface shall not be greater than the width of the reticle line. The maximum number
of dirt particles appearing within a central field of view of 50 mils diameter shall be three
(3). The maximum number of dirt particles appearing outside this field of view shall be
three (3). The minimum separation between dirt particles shall be 15 mils according to the
reticle. Dirt particles with widths and/or lengths less than ¼ of the reticle line width shall
be ignored regardless of distribution.
3.6.2 Other defects. There shall be no evidence of moisture, grease, fingerprints,
condensates, dirt, debris, scratches, fractures and adhesive separations when viewing
through the objective end of the instrument or on the surface of the eyepiece lens.
3.7 Optical characteristics.
3.7.1 Eyepiece focus. The best eyepiece focus of the reticle image shall be fixed
between the limits of -0.50 and -1.00 diopters. The variation in eyepiece focus between the
horizontal and vertical image shall not be greater than 0.25 diopters.
3.7.2 Parallax. Parallax at the center of the field shall not be greater than 0.25 mil
when viewing a target at 80 ± 10 meters.
3.7.3 Reticle accuracy. The angular separation between the 40 mil graduations on
the horizontal axis shall be 80 ± 0.5 mil.
3.7.4 Resolution. The resolution on the optical axis shall be 15 seconds of arc or
less when using an observation telescope of at least 3 power and entrance pupil of at least
0.4 inches. Resolution consists of detectable line structure and proper line count in all four
meridians. Total spread in focus shift between meridians shall not be greater than 0.25
diopters as measured at the eyepiece.
3.7.5 Parallelism of reticle and image. The vertical reticle line shall be parallel to
the image of a vertical target line and shall not be greater than 30 minutes of arc (8.89 mils)
at the position established in paragraph 3.4. This requirement shall also be met with the
elbow assembly positioned against the right and left swing stops and at the azimuth settings
of 4800 mils, 0000 mils and 1600 mils.
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