MIL-DTL-48558 Telescope, Elbow - M138A1This specification covers Telescope, Elbow: M138A1, which is one type of elbow telescope that provides an eight power magnification and an eight degree field of view. The telescope has a mil scale reticle for setting elevation. The reticle pattern is illuminated with a battery powered system.

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MIL-DTL-48558C

There shall be no dirt within the optical system which interferes with observation or

adversely affects image quality.

3.10 Operability.

3.10.1 Torque of diopter adjustment. The running torque required to operate the

diopter adjustment shall be within the values specified in Table II at the corresponding

temperatures.

TABLE II. Diopter adjustment torque.

Temperature

Torque required

+60�F to +90�F

5 to 9 inch pounds

-50 � 5�F

25 inch pounds maximum

+145 � 5�F

25 inch pounds maximum

3.10.2 Attachment. The elbow telescope locking mechanism shall be operable

when exposed to the operating temperatures of 3.5.2. The telescope shall be retained in a

manner representative of its use on the Mount, Telescope M172A1.

3.11 Reticle illumination. The reticle markings shall be clearly distinguishable

when observed in ambient light conditions ranging from dusk into darkness.

3.12 Interchangeability. Telescope interchangeability shall be verified by the

insertion, seating, and subsequent removal of a maximum fit gage.

3.13 Workmanship. Workmanship of the elbow telescope shall be in accordance

with the requirements of MIL-F-13926 and MIL-PRF-13830.