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| MIL-T-81333A(OS)
3.3.8 Eyepiece focus. Each eyepiece of this telescope shall be capable of being focused from plus 1 to minus
2 diopters by rotation of a ring or knob which moves an internal lens component. A focusing scale and index shall
be provided. Each line of the focusing scale shall be correctly located within 1/4 diopter and each interval correct
within 1/4 diopter. The eyepieces shall be airtight.
3.3.9 Filters Each optical system of the telescope shall be provided with a variable density polarizing filter,
so arranged that when the planes of polarization of the two plates in each filter are parallel, this common plane
shall be so oriented as to reduce surface glare in the target field to a minimum. A single-knob control shall be
provided which simultaneously operates the filters in each optical system of the telescope. The polarizing filter
shall comply with MIL-F-1424.
3.3.10 Interocular adjustment. Provision shall be made for manual adjustment of the intercular distance from
58 to 72 millimeters by movement of a control lever or knob. A scale graduated in 2 millimeter internals shall be
Provided. The interpupillary distance indicated by this scale shall be correct to within 1/2 millmeter.
3.3.11 Accuracy. The accuracy requirements with respect to elevation and depression of the line of eight shall
be as follows:
a. The plane established by the line of sight from -25 degrees to +95 degrees shall be perpendicular
to the plane formed by the four horizontal machined surfaces on the feet of the telescope body casting
within one minute of arc.
b. The plane established by the line of sight from -25 degrees to +95 degrees shall be parallel to
the plane formed by the two vertical machined surfaces on the left feet of the telescope body casting
within one minute of arc.
c At ny elevation or depression, the elevation of the line of sight with respect to plane formed
by four horizontal machined surfaces or the feet of the telescope body casting shall correspond to the
amount of rotation of the input shaft within two minutes of arc.
d. The above requirements shall be met at either magnification, with the variable density filters set for
any value of transmission in the telescope field of view and also with these filters removed, i.e., clear.
Machining of the mounting surfaces of a telescope after assembly of the optical parts therein, in order to secure
proper alignment, will not be permitted.
3.4 Environmental requirements.
3.4.1 Shockproofness. The telescope shall exhibit the degree of shockproofness required for the appropriate
grade classification, and class of equipment specified in MIL-S-901 as follows:
Grade A
Degree of Shockproofness
Equipment classification
Subsidiary component
Equipment class
Class I
Test classification
Lightweight
Type B
Type of test
3.4.2 Vibration. The telescope shall be capable of withstanding Type I environmental vibration as set forth
in MlL-STD-167.
3.4.3 Temperature and humidity. The telescope shall be capable of withstanding without damage or impair-
ment of performance temperature and humidity extremes as specified in MIL-STD-210 for worldwide shipboard
operation or as specified for Class 2 equipment in MIL-F-18870. The telescope shall also withstand temperature
and humidity conditions of short-term storage and transit as set forth in MIL-STD-210
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