MIL-PRF-13830B
better. Field and collective lenses shall have a surface quality of 20-5 in the central
zone and 40-15 in the outer zone. Center lenses of oculars shall have a surface
quality of 40-15 in the central zone and 40-20 in the outer zone. Eyelenses, excepting
those in symmetrical eyepieces, shall have a surface quality of 40-20 in the central
zone and 60-30 in the outer zone. When the field and eyelens are identical, the
surface quality for both shall be 20-5 in the central zone and 40-15 in the outer zone.
Filters which lie between the eyelens and the exit pupil shall have a surface quality of
40-20 in the central zone and 60-30 in the outer zone. Filters which lie internally
shall have the same requirements as specified for prisms in 3.7.10.1. Filters located
in front of the objective shall have a surface quality of 80-50 or better.
3.7.9.2 Fractures and edge chips. Edge chips which do not encroach on the free
aperture of the lens shall be allowable, providing the chip does not interfere with the
sealing of the lens in the mount. The surface of all chips larger than 1/2mm, as
measured at the largest extremities, shall be "stoned" to roughen it and lessen the
possibility of annoying reflections and additional chipping. The sum of the chip
widths of chips larger than 1/2mm, as measured at the edge of the lens, shall not
exceed 30 percent of the perimeter. Fractures in any face or edge shall be ground out.
Ground out areas shall remain within the applicable stoned chip limits of this
paragraph. Stoned chips and fractures in ground faces whose total summed up areas
are in excess of 2 percent of the area of the ground face or which are in excess of 2mm
depth shall be cause for rejection. Such stoned chips and fractures shall be cause for
rejection when they interfere with the optical path, mounting or sealing methods
regardless of their size.
3.7.9.3 Concentricity. Edges of all elements shall be trued to diameter about the
optical axis as a center by grinding. Lenses composed of two or more elements shall
be cemented and centered in such a manner that the axis of each element coincides
with the axis or axes of the other element or elements. Ocular lenses shall be
concentric within 6 minutes or arc, and all other lenses shall be concentric within 3
minutes of arc unless otherwise specified on the drawing or in item specifications.
After centering and cementing, mechanical eccentric glass overhang in excess of 50
percent diameter tolerance shall be removed. Optical eccentricity is defined as the
angular deviation, after refraction of an incident ray which is coincident with the
geometric axis of the lens.
3.7.10 Prisms and mirrors.
3.7.10.1 Surface quality. Surface quality of each prism shall be in accordance with
applicable drawings or instrument specifications. For surfaces which lie at least 15
diopters out of the focal plane, quality shall be 80-50 or better. For surfaces which lie
within 5 to 15 diopters of the focal plane the surface quality shall be 20-5 for the
central zone and 40-15 for the outer zone. For surfaces which lie within 5 diopters of
the focal plane surface quality shall be the same as for reticles.
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