DEAR ROBIN:

• Document Type: CREST
• Collection: NGA Records (Formerly NIMA)
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78B04747A001700010004-9
• Release Decision: RIPPUB
• Original Classification: K
• Document Page Count: 5
• Document Creation Date: December 28, 2016
• Document Release Date: April 23, 2001
• Sequence Number: 4
• Publication Date: February 12, 1965
• Content Type: LETTER

Approved For Release 2001/05/11 : CIA-RDP78B04747A0017R1 -?evlew by NIMA/DOD
STATOTHR
12 February 1965
I have looked into changing the anti-reflection coating to a
standard coating with higher reflectance values and tilting
the front glass. The coating manufacturer informed me that
the standard magnesium fluoride coating will reflect about 3%
instead of the 2/ for the special HEA coating of the optical
Coating Laboratory. The representative from OCLI agreed that
the standard coating will show less surface smudges than the
HEA coating, This coating is being procured along with tilting
the glass 7,
The 7? tilt is based on what is practical with the present
design, test results, and calculations. A short test was
conducted by placing a 10x10 glass plate (uncoated) in front
of a collimator. An observer was positioned in front of the
plate at the same distance he would occupy in front of the
viewer. With the glass untilted a person could not see himself
in the glass plate while looking into the collimator at a
target. Even glasses would not cause enough reflection to show
up. A virtual image was possible by holding a mirror over one
eye and reflecting the light back to the glass. By tilting
the glass 7?, this image was moved to the upper edge of the
10xlO plate.
The tilted glass also helps to eliminate reflection from 8ver-
head lights behind the operator. With the glass tilted 7 the
light could be as low as six feet and 12 feet behind the opera-
tor and still not be seen.
has been given the formal okay to start work
on Phase II, part 2. The completion date for this is 7 May
1965. I have also spent some time determining new specifications
for them. The overlapping method complicates the specification
when the gratings are tested as individual items without
overlap. Would Dick look the enclosed specifications over and
return them with any comments he may have. The attached sheet
provides basic data on the subject.
The vacuum hose and pump sound fine. We will have a connector-
on the viewer with a serrated connection to accept your hose.
When you return the specifications could you include the I.D.
of the hose you will use.
I will be looking forward to seeing you around the first of
May for the acceptance test, assuming you can send us a grating
the latter part of April.
Enclosures (2) STATOTH
Approved For Release 2001/05/11: CIA-RDP78B04
Sincerely,
 Approved For Release 2001/05/11 : CIA-RDP78BO4747AO01700010004-9
3.0 REQUIREMENTS (addendum)
3.1 The technical design goals of the 10x10 transmission
grating replicas which are to be produced during the second try
of Phase II shall be as follows:
3.1.1 Wavelength band to be used - 5086A. Test
grating at 5000 - 5500A. For intensity data intergrate results
from 5000 - 5500A?. Angular deviation measurements shall be
measured at 5086A?.
3.1.2 The grating shall disperse a total of 27 orders
consisting of the central order and 13 orders on each side of
center to the required amounts as stated in Section 3.1.3. Any
additional orders are acceptable, but they should not detract
from the transmission values required.
3.1.3 The nominal angular deviation of the central ray
in each exit pupil of the various orders shall be:
First order:
25'
Second order:
49'
Third order:
1?
13'
Fourth order:
1?
38'
Fifth order:
2?
2'
Sixth order:
2?
27'
Seventh order:
20
51'
Eighth order:
3 0
15'
Ninth order:
3?
40'
Tenth order:
4?
4'
Eleventh order:
4?
29'
Twelfth order:
4 0
53'
Thirteenth order:
5?
18'
The tolerance for each of the above deviations shall be
+3 minutes.
Approved For Release 2001/05/11 : CIA-RDP78BO4747AO01700010004-9
 Approved For Release 2001/05/11 : CIA-RDP78BO4747AO01700010004-9
3.1.4 Intensity Variation
When two crossed replicas are used, the light intensity
variation over the exit pupil matrix field shall be no greater
than 4:1. Due to the overlapping of the exit pupil orders the
light intensity variation between discrete orders need not be
the 4:1 ratio of the combined system. Due to the overlapping
in both X and Y planes a complex arrangement exists.
When individual readings are made of the transmission in
each order, the following formula converts any set of individual
readings to the value obtained when the gratings are crossed
and exit pupils are used at 50% overlap.
T _ 2 (Ta x Tb) + (Ta) 2 + (Tb) 2
ab
where Tab is the transmission of 4 combined orders. Such
Order:
Xaxis#
Yaxis#
Combinations:
4
4
5
4
4
5
5
5
then T = 4
a
Tb = 5
3.1.5 Number of order combinations. With a +13 order
system there are 676 order combinations.
3.1.6 The minimum transmission in any of these 676
order combinations shall exceed .0225%. This corresponds to
the 3% for a single order in the previous specification.
Approved For Release 2001/05/11 : CIA-RDP78BO4747AO01700010004-9
 ApproMe For Re lease MJ'L/QP/11 : CIA-RDP78BO4747AO01700010004-9
BY.----------- - - _ -------- _ ------------------------ SHEET NO-
0 a 4 6 Q 10 12
OF
7So'
OWER LAP /4PPR,A CN
I 3 5 7 9 to 13
6 1 a 3 4 5 G
.=-X/,r pupils
EACH PUPAL . a g g x, a 9 9 /itKHFS
..4-r 3.6 9,) h .-
Tor L tX/7 PUPIL 11V107-11 UAI r, SR
CQA/rr oL OF 5PEc1 FiCArlUN
X) -) Y Ii
C`f/T av,~~L ? 1'1(2P4
ova GAS AREA
/43 x'. /4Z 'N.
1?E44t'pw iH if OF
--Cow 9.uvE,0 IF x!1 PUPILS
STATOTHR
FOUR. Fx,r P/PIL
Duce L,4";, tc
Fog-m /N!?~
CUM QI'y; D
ST/aAIDAR0 METHoQ
X1i -Y Y I)
1
-mot- 11111
1 1 ~Q _ 1
-++r;-
X1)Yg
K0 Y O,
TYi'DlC/4L
E xi r
OVERLAP
Approved For Release 2001/05/11 : CAA=RDP'?8B04747AO01700010004-9
 Approved For Release 2001/05/11 : CIA-RDP78BO4747AO01700010004-9
MEMORANDUM FOR: Robin
I have honestly tried to understand Ray's
formula for T and to determine what it really
means. I have had absolutely no success, either
in deriving the formula or interpreting it.
If I have this much troutle, maybe he'd better
be a bit more explicit in defining his terms, and
what he means. Or perhaps this is an indication
of how far my 3aathematical skills have slipped.
In item 311, I believe the trial grating is
still 2 x 2 ih size - he may be looking ahead.
STATOTHR
16 Feb 1965
DATE)
FORM
MAYF BEM US10-101
AUGH 54 IQI WHICH REPLACES
ED.
Approved For Release 2001/05/11 : CIA-RDP78BO4747AO01700010004-9