2
3.4.2 Infinity sight- The image shall be clear, well defined and free
of objectionable imperfections. It shall resolve one half minute.
3.4.3 Image quality shall,
When specified, be equal to or better than
that of a periscope furnished or designated by the contracting officer,
3.5 Collimation (Seven power).-
3.5.1 When two parallel rays pass through the head prism and are projected
into the two objectives respectively, the conjugate rays emerging from the two
eyepieces shall be parallel within the following limits at the infinity focus
of the eyepiece and for any setting of the Interpupillary distance scale between
58 and 72 mm as follows:
Fourteen minutes of arc (2.0 minutes of true field) in the direction
perpendicular to the plane determined by the two entrant rays.
They shall not diverge sore than twenty-eight minutes of are (4.0
minutes of true field), nor converge more than fourteen minutes of arc.
(2.0 minutes of true field) in the plane .parallel to a plane formed
by the two entrant rays.
3.5.2 The line of sight through the center vertical reticle line shall
be perpendicular within 3 mils to the axis joining the two mounting holes.
3.6 Image tilt (seven power) .- The image of a plumb line formed by the
two eyepieces and as checked by an auxillary collimating telescope adjacent to
each eyepiece shall not exceed the following tolerances:
45 minutes of arc of verticality
o
(2.3 nil when measured across 10 field)
30 minutes of parallelism
o
(1.5 mil when measured across 10 field)
o
3e7 Parallax.- When viewing a target at 75 plus or minus 50 yards, there
shall be no parallax between the image and the reticle at the optical axis.
3.8 Plumb of reticle .- With the periscope vertical, with the axis joining
the two mounting holes in a horizontal plane and sighting through the peri-
scope: The broken reticle line shall not deviate from a horizontal target line
by more than the angle subtended O.4 mil at the extremity of the horizonal
reticle line, when the other extremity of the reticle line is in coincidence
with the horizontal target line.
3.9 Reticle accuracy .- The angular value between the zero point and any
other graduation shall be aS indicated within one percent plus 0.25 mil.
3.1O Eypiece focus ,- The diopter scale index shall indicate zero within
plus or minus 0.25 diopter when the reticle is brought into sharp focus with
the aid of a dioptometer of at least 3 power or an equivalent auxiliary tele-
scope. From this sharp focus the eyepiece shall have at least 2.5 diopters
movement in both the plus and minus direction.
(No. 51-72-71)
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