PROJECT 135 - OPTICAL SYSTEM

• Document Type: CREST
• Collection: NGA Records (Formerly NIMA)
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78B04747A001600010090-5
• Release Decision: RIPPUB
• Original Classification: K
• Document Page Count: 8
• Document Creation Date: December 28, 2016
• Document Release Date: May 2, 2011
• Sequence Number: 90
• Publication Date: November 1, 1965
• Content Type: MEMO

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Refer: R11-985
To:
cc:
Systems Management & Engineering Dept.
Digital Controls & Electronics Section
Subject: Project 135 - Optical System
From: F. S. 1 November 1965
This memorandum has been generated to establish the background and to
discuss the solution to the technical problems encountered in the develop-
ment of the optical system for the Universal Data Block Reader.
ACCURACY REQUIREMENTS
Section 4. 4. 3 of Proposal SME-PR-09 outlined the method by which the reader
would correct for wander of the film in both the camera and the reader itself.
This system employed a read head containing 108 diodes, each spaced . 006
inches ap.rt. The diodes are grouped in three sets, A, B, and C creating
three separate heads, interlaced with each other. As the film wanders, the
distance betwed;n the edge of the film and the index bit of the data block will
vary. A window of 12 diodes, 4 of each group, is aged to locate the index
bit. Since the wander varies continuously, and the resolution of the head is
. 006", the index bit may fall under any one or more of the 12 diodes in the
window. Ideally, with a perfect dimensional match between the diode array
and the data block, when the window picks up an index dot with a diode belong-
ing to one group, all dote in the data file will also be picked up by the diodes in
the same group. In actuality, a perfect match cannot be achieved and certain
tolerances have to be considered. The following analysis will establish the
maximum tolerable dimensional deviation which allows reliable reading.
The smallest geometric coverage of any diode will occur when the minimum
size dot of . 006" will be evenly covered by two adjacent diodes, such that
each diode will see one half of a dot or . 003" of area coverage. The threshold
of the read amplifiers is set to recognize .002" of coverage as a dot. There-
fore, if any one diode group is selected, only . 001" total deviation from nominal
is allowed between the index -dot image and the image of any other dot in the
data block. By changing the logical scheme to one in which a split coverage of
a dot by two adjacent diodes activates both diode groups, the allowable tolerance
is doubled. This will effectively widen the pickup area of each head increment
to.012" instead of the .006" of a single diode.
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vow,
Refer: R11-985 Page -2-
1 November 1965
Under this scheme, the worst case condition is no longer the one described
previously. Instead, the tightest dimensional accuracy will be required when
a .006" dot will be covered unevenly by two diodes - one diode covering . 004"
and the other . 002". Because- of the amplifier threshold, the diode covering
the . 02" portion of the dot is on the verge of being ignored, and only one diode,
the one with the . 004" coverage, will provide a reliable output. Under these
conditions, only one diode group will be selected, and the tolerable dot devi-
ation is .002".
Since the diode array is dimensionally accurate to . 0003" and the film shrink-
age can reduce the recorded block by . 0002", the system has an inherent basic
inacurracy of .0005". Allowing another . 0005" for film thickness variations
and a safety margin, a tolerance of . 001" is left for the optical system.
completely in the blue region of the visible spectrum.. Therefore, the focus of the
ADAS lens is corrected for blue light. The silicon photodiode response unlike
that of panchromatic film, lies in the infrared region. The ore, the Universal
Data Block Reader will Ampl y a un sten lama as a light source to closely match
the response of the diode. To provide optimum results, the lens employed in the
reader must be corrected for a portion of the red region of the spectrum. How-
ever, initial testing of the read head using the ADAS lens indicated that sufficient
signal was present and it was decided to use the AD
AS lens for breadbo di r
light given off by'the particular phosphor used in the u Gated
ray tube as a light source and imaged. t urce on panchromatic fi m. e
When the optics for the Universal Data Block Reader were initially considered,
it was known that a lens similar to that employed in the Imo',-56 camera for the
ADAS system would be necessary. Due to the tolerances of the data block,
both systems require a low distortion lens. The ADAS system utilizes a cathode
A
ar ng
rye { p u r p o s e s only, with a detailed analysis to follow at a later date to insuretat the
De acceptable. Whether or not the distortion was acceptable wou d no of ; ec
At this writing the analysis of the distortion characteristics has been completed.
It has been found that the ADAS lens, while satisfactory in the blue region, of the
visible spectrum for which it was originally designed, when used in far red (and
infrared) region creates a condition which is marginal from a system viewpoint.
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TWO,
Refer: Rll-985 Page -3-
1 November 1965
The lens exhibits approximately .012" (computed), .016 rnieasure4 axial focal shift
over the spectral region of 0.450 mu to 0. 800 mu. This is considered excessive
for two reasons. One is the effect it will have on the image size and the other is
the effect on magnification. The chromatic growth of the image of a dot will be
in excess of that defined by the system requirements. It will be in excess of
001" on the diameter. If one considers the full change in scale (magnification)
with wave length, i. e. 1? x 100% _ . 6% it can be shown that this exceeds
the required position accuracy of the system. Therefore, the ADAS lens would
seem to be one which is not capable of providing a usable image for this particu-
lar system.
PROGRAM IMPACT
From the aforementioned analysis it is seen that a low distortion mapping type
lens, corrected in the red region, is required. While the technology for design-
ing and manufacturing such a lens exists, the need for this type of a lens, to
our knowledge, has not arisen in the past. Therefore, a now lens must be
designed. It is the opinion of the writer that this new requirement will delay
Phase I of the program approximately three (3) months. The physical time of
performance of Phase II should not be affected. However, the starting time
will be delayed by the amount of time that Phase I slips.
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Systems Management & Engineering Dept,
Digital Controls/ElAtronics Section
To: Subject: Scanning e Array
From: C. P, H. S.
This memo will describe the equivalent circuit and operation of a scanning
photodiode array supplied by the Transducer Research section
Also included are experimental results obtained operating the device.
The array features 50 photodiode elements which are scanned to produce a
single serial output. The scanning is performed by the application of a
voltage waveform consisting of a ramp or a staircase.
Figure 1 illustrates the equivalent circuit of the array and its connection
into a circuit. The collector to base junctions of transistors Q1 through
':?50 act as photodiodes when reverse biased. Light generated charges
act as base currents turning on the transistors which supply amplification.
The bias supply generates a potential drop accross the distributed collector
resistor making the collector potentials of transistors Ql through "-50
progressively lower. The output of the scan generator at the start of oper-
ation applies forward bias to the collector to base junction of transistor
Q1. This is true for each transistor and the junction cannot act as a photo-
diode. The base to emitter junctions meanwhile are all reversed biased
preventing the flow of current in the output line.
As the sweep voltage increases, the collector to base junction of 01 will
become reverse biased and act as a p-otodiode. Light generated current
will act as a base signal and is amplified. The amplified current flows in
the output line. As the sweep voltage becomes progressively larger, the
other transistors will sequentially operate.
The device supplied b Iliad junctions with active areas of 0. 003 inches LJ" I
by 0.007 inches placed on a 0. 010 inch pitch. Figure 2 illustrates the measured
transfer gain of the array. The experimental circuit shown in Figure 3 was used.
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Refer: F12-191 Page -2-
4 March 1965
The experimental data indicates an element output of current of 750 nano-
amperes for a 50 foot candle input. The calculation for the theoretical
expected value is given as:
i=IKDAIg
I = light intensity (50 ft. candles)
KD = diode constant (30 x 10-12 ampere/ft. cand/sq. mil)
A = diode area (21 square mils)
'S = transistor gain (Z5)
i=790x10-9 amperes
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w
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Sweep 4-1~
3 Y Pk-~k
FIGURF 3 ExPERINIE'J AL SETUP
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{
}
16oo
Iy00
1200
1000
Sao
600
yvo
100 i1S 150
LIGHT INTENSi T Y (Foot C v)d Ies)
C NNIN PHo T OLIODE ARRAY
TRANSFEK ' P%!
NOW
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