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shall not exceed 1 per cubic centimeter (0.061 cubic inch). In no
case shall the mean diameter of any individual bubble exceed 0.021
inch. (0.58 millimeter).
D-2c. Striac shall be light and scattered when viewed in the
direction of maximum visibility. The striac shall be just above the
limit of visibility..
D-2d. Color characteristics of a specimen or specimens within a
thickness range of 1.5 to 3.0mm, representative of a lot of plates
shall conform to the requirements of section E.
D-3. Formed blanks.
D-3a. Dimensions - Thickness shall be as specified in the con-
tract with in the following tolerances:
Tolerance Of thickness
Diometer of blank
Plus
Minus
0 mm
3 mm
10 mm to 40 mm
0 mm
4 mm
41 mm to 75 mm
Unless otherwise specified, blanks shall be circular. Diameters
shall be as specified in the contract within a tolerance of plus 2 mm
minius 0.
D-3b. Limiting sizes of defects.
D-3b(1). Formed blanks intended for use as a finished filter
which lies internally in an optical system shall not contain more
than one bubble, seed, stone or inclusion visible to the unaided eye.
No defect shall larger than 0.008 inch (0.23 millimeter) in mean
diameter, tanks othemwise specified on the drawing to meets better
D-3b(2) Formed blanks intended for use as a finished filter
which lie between eyelens and the exit pupil of an optical sys-
tem not contain bubbles larger than 0.008 inch (0.20 milli-
meter) in diameter and in other formed blanks the bubbles
shall not be larger than 0.020 inch (0.50 millimeter) in mean diam-
ster. The total projected area of the bubbles visible to the un
added eye shall be not more than 0.025 percent of the projected
area of the blank except that then may be at least one bubble per
blank but never more than eight. All bubbles shall be scattered.
D-3c Color characteristics of a specimeno or specimens within a
thickness range of 13 to 3.0 mm, representative of a lot of formed
blanks shall conform to the requirements of section E
D-3d Striac-Shall be light and scattered when viewed in the
directtion of maximum visibility. The striae shall be just above the
limit of visibility
D-4 Finished ray filters.
D-4a Dimensions shall be as specified on the drawing.
D-4b. Limiting sizes of defects shall be as specified on the draw-
ing or as specified in U. S. Army Specification No. 51-70-2.
D-4c. Color characteristics of a finished ray filter within a thick-
ness range of 1.5 to 3.0 mm shall conform to the requirements of
section E.
D-4d Strias. - The finished my filter shaIl contain no visible
striae.
(No. 51-73-92)
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