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MIL-T-50760(MU)
13 August 1971
3.5.3 Sealing. - The telescope shall show no evidence of leakage in
excess of 0.2 psig when subjected to an internal pressure of 5 0.10
psig for a period of 2 hours using dry nitrogen having a dew point at
least as low as -25F.
3.5.3.1 Condensation (low temperature). - When view
through the eye-
piece and objective ends of the telescope, there shall be
no evidence of
condensation at room temperature (60 to 90F) immediately
upon tehermal
stabilization, subsequent to being subjected to the -80F
and prior to the
+16F requirement of 3.5.1.
3.5.4 Cleanliness. - The telescope shall meet the cleanliness require-
ments of MIL-O-13830. When viewed through the eyepiece, dirt shall not ex-
ceed the following limitations of dirt, quantity, and size (see 6.33-size
equivalent).
a. Inner zone (100 mils diameter). - The maximum size of any one
particle of dirt or foreign material shall not exceed the area equivalent
to a size 5 dig. There shall be no more than 6 particles of dirt. Three
particles may be as large as a size 5 dig. Three particles shall not ex-
ceed a size 1 dig. Any particles smaller than a size 1/4 dig shall not
be counted.
b. Outer zone (limited to clear aperture of reticle). - The maxi-
mum size of any one particle of dirt or foreign material shall not exceed
the area equivalent to a size 10 dig. Three paricles may be as large as
a size 10 dig. Smaller sizes may be more in number, but their combined
area shall not exceed that of 3 size 10 digs, which is maximum dirt per-
mitted. Any particles smaller than a size 1/4 dig shall not be counted.
c. Dirt separation. - The separation between each dirt particle
or foreign matter shall be at least 10 mils for both zones.
d. Glass surfaces. - All glass surfaces shall be free of conden-
sation, or stains resulting from condensation, when viewed through the
objective and eyepiece ends of the telescope.
3.6 Accuracy.
3.6.1 Collimation. - The optical axis of the telescope shall be in
coincidence with the geometric axis within 0.50 mil when the telescope is
rotated 3200 mils (90 to the left and 90 to the right from a vertical
position of the eyepiece) about the geometric axis as defined by the ex-
terior mounting surface of the objective tube of the telescope.
3.6.2 Parallax. - With the parallax shield removed, parallax at the
optical axis shall not exceed 0.2 mils when viewing targets between 300
meters and 1000 meters.
3

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