No. 51-72-71
U. S. ARMY
SPECIFICATION
Amendment 2
5 April 1949
Superseding
Amendment 1
PERISCOPE, M15
The following Change 9 shall be made in U. S. Army Specification No.
51-72-71, dated 26 January 1949:
Page 1, Paragraph 3.4.1. and 3.4.1.1 Delete and substitute the
following:
"3.4.1 Seven Power System. - Resolving power on the axis of both
telescopic systems for a parallel bar test object shall be 3,5 seconds of
arc, or betters."
Page 2, paragraph 3.4.3. Delete.
Page 2, paragraph 3.7. Delete and substitute the following:
"3.7. When viewing a target at 750 plus or minus 50 yards with the
-
aid of an auxiliary telescope of at least 3 power focused at infinity, the
eyepieces shall indicate zero diopter within l/4 diopter."
Page 2, add the following paragraph.
"3.7.1. The dioptric difference between the Image of the target
and the reticle graduation nearest the optical axis shall be between
zero and minus 0.3 diopter when measured on the eyepiece scale."
NOTE: This condition must be met when using a head prism having no
spherical power, or by adjusting for parallax without the head prism.
Correction of fault indicated by failure of image to focus when eyepiece is
within l/4 diopter of zero must be made by focusing objective.
* Page 2, paragraph 3.10. Delete.
* Page 3, paragraph 3.10.1 Renumber this paragraph to read 3.10.
*
Page 3, paragraph 3.11.2. Delete & SUbstitute the following:
"3.11.2. With a periscope adjusted to meet the Prallax requirements
of paragrpah 3.7$ the parallax between the reticle graduation nearest the
optical axis and the image target at 750 plus or minus 50 yards, intro-
duced by Interchange of heads, shall not exceed diopter."
Page 3, add the following paragraph 4.3.
Image Quality (Seven Power) -The test object shall be of
"4.3.
the pattern illustrated in U. S. Army Specification No. 51-70-2, figure
VI-A. The image shall be viewied with the aid of an 8 to 10 Power auxil-
ary telescope of approved design, scaled in diopters. The test pattern
shall be resolved in each of the four meridians by an adjustment of the
auxilary telescope not to exceed ± l/8 diopter from the setting for best
focus on the numeral in the center of the test field."
*Asterisks indicate changes from previous amendments.
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