MIL-DTL-48550A
4.5 Sealing. Internal pressurizing of the collimator to test for sealing shall be
performed using nitrogen gas having a dew point of -25°F or lower, and commercial type
pressure testing equipment capable of pressurizing the collimator to the pressure specified
in 3.5. The test equipment shall be equipped with a pressure shut-off valve, filter, and a
calibrated pressure gage to read required pressure value specified in 3.5 to an accuracy of
±.02 psi. Maintain the pressure within the collimator for the period specified. Any drop in
pressure as indicated on the pressure gage of the test equipment shall not exceed the
requirement specified in 3.5. The pressure shall then be reduced to zero psig (normal
atmospheric pressure). The collimator shall then be flushed with dry nitrogen until the
interior atmosphere has a dew point at least as low as -25°F. When this atmosphere is
attained within the collimator, the unit shall be sealed with an internal pressure of nitrogen
at a pressure of between 0.25 and 0.50 psig at room temperature, +60°F to +90°F.
4.6 Optical.
4.6.1 Reticle lean. Reticle lean test shall be performed with aid of a collimating
telescope, hereafter referred to as auxiliary telescope; with a reticle plumbed and adjusted
to infinity focus. Position the collimator in front of the auxiliary telescope so the optical
axes are coincident. Align the zero vertical line image of the collimator parallel with the
vertical line image of the auxiliary telescope. With the zero vertical line image of the
collimator plumbed, the bubble of the level vial shall be within the central graduation
marks of the vial in accordance with the requirements of 3.6.1.
4.6.2 Reticle accuracy. This test shall be accomplished with the aid of an auxiliary
telescope and calibrated reticle pattern. The calibrated reticle pattern shall have a
horizontal line 100 mils in length with vertical marks at the center and each end. A mil
block at either end of the horizontal line will enable the observer to detect error. With the
auxiliary telescope focused on the collimator reticle image, both 50 mil marks of the reticle
image shall coincide within the allowable tolerance in accordance with the requirements of
3.6.2.
4.6.3 Parallax. This test shall be performed with the auxiliary telescope positioned
as specified in 4.6.1. Parallax shall be removed from the auxiliary telescope by means of
an auto collimator. The test shall be made by sighting through the auxiliary telescope to
the collimator center cross image. Parallax will be recognized as any apparent
displacement of the collimator center cross image in relation to the auxiliary telescope
reticle when the observer's head is moved from side to side, or up and down. Any
movement of the observer's head shall not cause displacement of the collimator center
cross image to exceed the requirement specified in 3.6.3.
4.6.4 Cleanliness. The optical system of the collimator unit shall be inspected for
cleanliness in accordance with MIL-PRF-13830 and 3.6.4 and shall meet the requirements
specified therein. Dirt particles which interfere with the legibility or accuracy of the reticle
pattern shall be cause for rejection. The mean diameter of a size 10 dig is equal to 0.10
millimeter.
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