IMPROVED REAR PROJECTION VIEWING SYSTEMS

• Document Type: CREST
• Collection: NGA Records (Formerly NIMA)
• Document Number (FOIA) /ESDN (CREST): CIA-RDP79B00873A001600010003-4
• Release Decision: RIPPUB
• Original Classification: K
• Document Page Count: 64
• Document Creation Date: December 28, 2016
• Document Release Date: September 11, 2012
• Sequence Number: 3
• Publication Date: January 13, 1965
• Content Type: MISC

I A ?TAT '
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'W.V. ? 0.4
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Attention: John R.
Gentlemen:
15 January 1965
We are sending you the enclosed rough draft at your request in a
partially edited form. Some discontinuities are still evident but
thought you would like to have it as soon as possible. We will
continue here to make a smoother version of this for final presentation
and will look forward to receiving your recommendations as soon as possible.
Perhaps the quickest way of transmitting information is to mark up the
extra copy and send it back with your comments.
Please call on
Sincerely,
if you need help getting things back and forth.
Program Manager
WD$Osf
STAT
STAT
STAT
STAT
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Register No. 23-2554A STAT
IMPROVED REAR PROJECTION
This proposal is presented by
tion of the
day rear projection viewing system.
VIEWING SYSTEMS
with the coopera- STAT
to extend the capability of the preseSTAT
The proposal recommends the extension of the
fluorescent screen development and provides for additional research in the areas
of electro-chemical and chemical screen development, band width limited physical
optics, light sources and computer interface displays.
Considerable attention has been paid during the prior feasibility study to the
possible outcome of a program of this type. As a result of
will be found in the body of this proposal several research
applicable.
this thinking, there
reports which are
has long been searching for an information system regardless of STAT
the media to reproduce the data contained within the confines of a simple 23/4" x
2k" film negative. It is not difficult to see that the criteria which any infor-
mation system needs to meet to equal a visual photographic capability needs
extremely wide band width and, as a result, very high frequency. Storage of a
single 23/4"?x 23/4" film negative with high resolution in a computer memory system
may require as much as 50 billion bits of information. The proposal discusses
means to decrease the storage capacity through discrete scanning techniques in
1
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selection of what we term "foveal memory areas". A report will also be found
discussing the known means for transmission of film negatives through television
channels.
It is in this area that we find theFZ;-wid_6aestrictions limiting the amount
of resolution which is capable of being handled by typical cathode ray tube
systems. EaLr 1:-.0-f-5-elf6---zo-fda-- of Afta kilo-megacycLeS",haire_t:-b?efIrnate-d-to?b-e
recessary to provide the-reproductioni-og-high-tesolu-tion In directing
comparison is the physical optical reproduction which utilizes the infinitely
broad band width of the light beam to transmit the required detail. In other
words, photographs may be reproduced by electro-sensitive phosphors to the degree
necessary for recreating high resolution if transparent phosphors are used but the
state-of-the-art limits the band width capabilities necessary to convey the infor-
mation from the film to the phosphor. It is felt that these technologies are not
to be overlooked for certain specific purposes such as the recognition of details
once it has been ascertained that there is some detail by scanning for prelimi-
nary examination of the film through an optical device. Thus, the proposal
contains a technical discussion on the use of cathode ray tube systems proposed
to enhance detail through the use of "unsharp masks" and to provide an eletronic
system for tone reversal.
The results shown by the newly developed fluorescent screens promise in themselves
to provide the information content necessary to fulfill the band width require-
ments. Limitations here are represented only by the efficiency of the light
sources available and the possibility for discrete enhancement of details within
the scanned area. There have been recent innovations which promise to point the
way towards the relaxation of these limitations. The body of the proposal contains
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Nige
L.
a research report describing a system which may be used scanning a laser beam at
kilo-megacycle rates. Again, the band width problem arises. Any system i1177517FLITg
Elie use of feedback_control faces th-n?liffitationmr.The systems may still have a
function, however, by providing masks or image enhancement when they are combined
with physical optical systems.
The most promising aspect seems to lie in the structure of photosensitive phosphors
and semiconductors used as screen materials and excited by projection systems
utilizing ultraviolet and visible light. The use of non-linear or superlinear
phosphors may provide a ready source intensity or electrostatic modulation of the
phosphor.
As mentioned before, the proposal divides itself into four categories of tech-
nology. A brief description of the contents of each of these categories follows:
SCREEN DEVELOPMENT
The fluorescent screen has proven itself by producing resolution capabilities
above 200 lines per millimeter at brightness levels which average from 5 to 10
foot lamberts highlight brightness.
erMOMMTOM???????101161?11.1
It is proposed that these screens t;_tested
for their lifetime capability and that a large screen (30" x 30") be constructed
using minimum tooling from the best material from consideration of brightness and
=======ft
lifetime. It is proposed that the field of non-linear phosphors and superlinear
...=s=p....
phosphors be examined for image enhancement purposes.
401%,
A new development in the field of non-organic phosphors has appeared throughout ?
7th(5 e addition of sodium to the fluorescent material to greatly increase the light
output in the lifetime of the phosphor. It is proposed that these systems be
examined. Electrostatic enhancement of the ultraviolet image is discussed along
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with the enhancement by electro-luminescence for the combination of a photo-
conductor phosphor two layer screen. In this case, a photocondpctor acts directly
upon the phosphor to enhance the image without the use of frequency limiting
electron feedback systems. An attractive advantage of this lies in the possibility
for electro-sensitive modulation of the phosphor. In addition to the direct
excitation of a screen by a light source, ?two methods for producing image enhance-
ment are described utilizing the assistance of a cathode ray tube which combines
an electric mask, the projected image of the film negative.
BAND WIDTH LIMITED AND SPECIAL PURPOSE OPTICS
Since the ultraviolet seems to offer the best solution to high resolution projec-
tion systems this proposal includes a discussion on zoom lenses to be utilized
over a 9%" format at minimum magnification and to be extended over an approximate
four to one magnification range for scanning purposes. Since the ultraviolet
system at present utilizes light sources which produce both visible and ultra-
violet light be divided after passing through the film for use in two separate
producing an image on a separate screen with visible light. New capabilities in
energizing the ultraviolet screen and the other a zoom lens for scanning purposes
lens systems, one which produces the high resolution at maximum magnification for
the use of Fresnel lenses for condensing the dichroic mirrors are proposed. The
0
design of mirrors for discrete reflections of the wanted wavelengths is proposed
to provide retension of at least 90% of the ultraviolet available from the source.
The proposal includes a discussion of the application of methods for the use of
aspheric design, the production of lenses having extremely high resolution capa-
bilities, and proposes that these lenses be tested utilizing the optical transfer
function techniques and ultraviolet sensors consistingphotomultij.jer tubes
in thefj2_)eE_9.p..tls_p_a,th of a microdensitameter having an apemu_al_less than
.06" diameter,
4
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LIGHT SOURCES
The system now in existence utilizes a 2500 watt mercury vapor compact arc lamp.
This lamp produces 8% of its total radiated power in the 2654 I region, but a
great deail of power is lost by radiation due to the heating of the electrodes.
It is proposed that a substitute be examined which has 10 times the ultraviolet
production efficiency and falls into the extended arc type. These extended arcs
have as much as 807. of their light output available in the ultraviolet region,
4 and if folded properly and focused as a semi-extended source can provide in those
72,2>
u traviolet energy. In addition, it is suggested that the internal coating of
the tube containing the extended arc be examined by the application of phosphors
which themselves produce an efficient cold source for ultraviolet energy.
Lasers are discussed as a means for providing a scanning system capable of
providing feedback controlled image enhancement ?Two-means for deflection of
the laser are discussed, one of which s the-typical ;err C 1, the other of
which is a recent patent application by
per taininESTAT
to the use of a laser in place of the typical electromagnetic galvanometer. The
plasma source is discussed for information purposes only and is regarded as least
promising due to the high energy consumption required by this source.
COMPUTER INTERFACE DISPLAYS
In this section a discussion of the limitations of the types of displays capable
for computer presentations' are discussed with regard to the quantity of memory
required to provide high resolution reproduction of such things as maps and
photographs.
has at the present a computer developed which operates on what STAT
is termed as 'foveal area memory". A brief discussion follows. For a totally
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L;)
scanned image of the typical film negative only discrete bits of information are
retained by the computer upon command. The computer is capable of being zoomed
to select any area of interest within the photograph and can utilize its photo-
memory capabilities over that particular foveal area. The computer will retain
image contrast levels particular to that area. These contrast levels can then be
compared to prestored memory images which are auto-correlated to an image in
storage. The system is presently used to identify satellites against a star
background. The interface
aperture 400" telescope by a scan by an image orthicon. It is operating at
at this time.
in this case is not a film negative but a field of 13"
DETAILED TECHNICAL DESCRIPTION
The presentations which follow have been generated by different individuals and
are presented as such. The distinct fields present areas in which research is
believed to be most rewarding in the improvement of rear projection viewing sys-
tems. Some of the areas cover extensions of the work now being done while others
propose new approaches, knowledge of which has been gained through prior experi-
mentation.
STAT
Chemical and Electrochemical Screen Development
STAT
6
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Noe
Image Intensification
A multiple layer system of photoconductor and electroluminescent phosphor may be
used to provide image intensification. The photoconductor should be sensitive to
u-v only or else there should be a barrier to visible light between the two layers
to eliminate positive feedback and a "runaway" condition.
Projected Ultraviolet Image
Electroluminescent Phosphor
Visible Output
Photo-conductor
The external surfaces would be coated with transparent conductors. The photo-
conductor would conduct when illuminated, applying a larger voltage gradient to
the phosphor than existed in the dark condition. The phosphor would then electro-
luminesce with an intensity determined by the excitation intensity.
Typically ZnS may be useful since it is not photoconductive in visible light but
is sensitive to ultraviolet. Therefore "runaway" would not occur due to roamlight
photoconduction or phosphor output feedback. By suitable doping, e.g., (ZnS:
Mn2Cl for 36501)(4) ZnS can be made to absorb with a peak at 36501. See Figure.
Emission as a function of wavelength
for zinc sulfide crystalline films9
5 - 15 microns thick,
C.)
0
04
0.)
RS :101.0
St4.Ni;01
10 ZERO
AT .-.0S0
?340
JW AN AW
Wavelength A (microns)
The use of the non-organic phosphors is not to be discounted. These components
are considered to be more stable than organic phosphors and thus much less sus-
ceptible to aging. In addition, the non-organic phosphors present more potential
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light output. It has been found that the transperent?ghn-sphors previously fabri-
__
:.? _------
- cated,in the research center lacked one essential ingredient, that ingredient is
--- --
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`------ __---_______---------
sodium. The addition of this element transduces?enexu levels necessary to high-
light output. Experiments with phosphors containing sodium
prove most
rewarding. Theoretically it can be shown that these phosphors will provide three
times the light output of the presently developed organic screen.
A two layer phosphor - photoconductor could be used to fabricate a fluorescent
screen, enhancement by electroluminescence. This would require a transparent
photoconductor sensitive to the emission spectrum of the phosphor. The photo-
conductor would be in contact with the phosphor and each of the two exposed phases
would have transparent electrodes. When the ultraviolet sensitive phosphor is
struck by ?light the resulting fluorescence would cause the photoconductor to
conduct, increasing the field across the phosphor and adding electroluminescence
to the existing fluorescence. It can be shown that assuming a 10% loss in trans-
mission due to each of the two electrodes and an additional 107. loss due to the
photoconductor and a developing of the light output of the phosphor due to
electroluminescence that the light available to the observer will be 140% of that
due to ultraviolet stimulation fluorescence alone. However, since the photo-
conductor is sensitive to visible light, the screen may have to be operated in
a roam with controlled ambient light.
Contrast Enhancement
Contract may may be increased or reduced, depending on the materials used, as a
function of the excitation intensity reaching the screen by utilizing superlinear
(1)
phosphors. These effects have been known for about 25 years. Riehl, Urbach,(2)
and others(3) have published on this subject.
8
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The intensity is determined by the absorption due to detail in the film being
rojected. The use of the superlinear effect may be understood as follows:
ppose the film to be projected contains a density step wedge having steps of
transmission increasing by 2 times from one to the next. A superlinear phosphor,
onto which radiation through the step wedge has fallen, would radiate with steps
having brightness ratios greater than 4 times from one to the next (since an
(3)
index of at least 2 has been re orted----Yr?In?th?rs--way at-r-ast_ixpul one step
to the next would be increased. Urbach showed that the effect discovered by
Riehl can be enhanced enormously, using a quanching agent, such as nickel, in a
ZnS phosphor. The deviation from linearity at highlight levels may be so large
that the luminescence yield is several hundred times larger than that at low
intensity. Factors which would have to be investigated would include absolute
intensity range and spectral region in which these effects may be produced.
By varying the intensity of the excitation source, the level of the range of
contrast enhancement may be selectable. See Figure.
TOUT
References
i
1
HIGHER CONTRAST RANGES
--...-.1";11?
LINEARITY
CURVE
ITN
(1) Riehl, N. "Uber einen neuen Effekt an lumineszierendem ZnS," Z.f. techn.
Phys. 20,152 (1939).
(2) Urbach, F., Urbach, A., and Schwartz, M. "The Brightness of Apparent
Fluorescence as a Function of the Exciting Intensity," J. Opt. Soc. Am.
37, 122 (1947).
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cc)
(3) Nail, M.R., Pearlman, D., and Urbach F. "Photoluminescence of Some Sulphide
Phosphors as a Function of Intensity," in The Preparation and Characteristics
of Solid Luminescent Materials, (Cornell Symposium of the American Physical
Society, October 24 through 26, 1946, John Wiley & Sons, New York, 1948.)
(4) Cusano, D.A., "Cathodo-, Photo-, and D.C. -Electroluminescence in Zinc
Sulphide Layers," in Luminescence of Or anic and Inor anic Materials.
Edited by H.P. Kallmann and C.M. Spruch. (John Wiley & Sons, New York,
c1962), P. 494-522.
Modulation of Phosphor Intensity
Electroluminescence may be excited by application of AC potentials. The photo-
conductor - electroluminescent phosphor sandwich model discussed in the section
dealing with image intensification, may be operated with AC upon which a variable
amplitude DC is superimposed. In this manner regions near threshold excitation
will be pushed in and out of the light emission region. If a suitable nonlinearity
of electroluminescent intensity with voltage can be obtained near threshold the
-contrast of low intensity detail may be increased. By analogy with vacuum tube
characteristic curves, a change
from another one of a family of
average intensity
aried.
Life Tests on Luminescent Materials
and hance the
in bias
curves.
region
voltage will shift the output to that
A shift of AC voltage will vary the
which the contrast is
/4
Previous work showed that most organic materials, and in some conditions inorganic
materials also suffered a reduction in luminescent output with exposure to the
excitation radiation. The mechanisms involved may in some cases be photochemical
change of molecules. In other cases, the charge may be due merely to oxidation
which occurs with or without ultraviolet but is quicker with ultraviolet.
10
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Life tests will be made on screens developed. In the case of luminescent
ultraviolet excited screens, a constant excitation intensity will be used and
output of the screen monitored. It will be necessary to use accelerated tests
which will show the relative merits of materials. In the case of electro-
luminescent screens accelerated tests probably are not applicable since output
can only be increased by applying greater voltage gradients than the phosphor
layer will support and breakdown will occur. In this case, there is no substitute
for time.
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PATENT DISCLOSURE
ELECTRONIC SYSTEM FOR TONE REVERSAL
This invention relates to the production of tone inversion for the
display of a positive picture from a.negative (or vice versa) with use
of an electron beam scanning technique.
Using a conventional television system a tone reversal may be produced
by connecting together a flying-spot scanner, a video amplifier with polarity
reversal and gamma correction and a picture monitor. The expenditure involved
is unnecessarily high as the potentiality for transmission over distance
inherent in the method is not required for a self contained unit.
The method herewith described and its variations involve only a single
cathode ray tube and simplifies the design substantially. The set-up in
its basic form involves a flying-spot scanning system in which the CRT,
unlike the usual procedure, is modulated by the signal derived from the
scanned image in such a way that light absorption creates an increase in
screen luminance for each individual picture element. A feedback amplifier
with adequate high frequency response, low phase distortion and short time
delay is connected between the photomultiplier and the brightness control of
the CRT. This amplifier works in such a way as to maintain a nearly constant
current output at the multiplier. The reversed image can be observed at the
CRT which thus serves a dual purpose.
A problem arises from the fact that phosphors with a suitably short decay
time have their emission located in the blue and ultra-violet part of the
spectrum, which makes it inconvenient for visual display.
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???.-st
A phosphor with a color more suitable for visual display will require an
electronic high-pass filter network to prevent excessive picture streaking.
It is probable that such a filter may produce a finite time lag which is of
no importance in television but would be detrimental for this particular use.
A second method suggested here is to utilize a screen made up of a
mixture of two distinct phosphors, one of blue and ultra-violet color and
very rapid decay for the scanning process and the other one of yellow-green
color without any blue or ultraviolet emission and of slower decay, for
visual display. The separation of the two light qualities is easily obtained=
with suitable filters.
A third approach is to make use of a somewhat more elaborate CRT re-
presented in a sectional view of a practical embodiment in the diagram.
Inside the glass envelope (1) of the CRT is a fluorescent screen composed
of two different phosphors with similar qualities as above mentioned, but in
two distinct layers) an outer layer (2) for visual display and an inner layer
(3) for scanning. The outer layer may become luminescent either by the impact
of electrons having passed through the inner layer, or by activation by the
light emission of short wave length of layer (2), or by the combined action
of both.
The screen is imaged through the flat section of the glass envelope (4)
on the transparency (7) by the lens (6) after reflection at the surface mirror
(5). The condenser (8) collects the transmitted light on the photomultiplier (9).
The amplifier (10) works in the manner described above. A visible pattern,
reversed in tone with regard to the picture (7), is made visible on the screen
and may be viewed at (12).
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For all described examples there is no problem in accuracy of scanning
or in electron optical imaging, as scanning and display are effected at
substantially the same location.
The feature of the feedback system adds the advantage of equalizing
unevenness of light distribution due to the irregularities of the screen
as well as amplitude distortions of the separate elements (multiplier unit,
amplifier and CRT).
Electronic reversal of motion pictures on film seems feasible using
either optical compensation and continuous film motion or a blanking time
compatible with conventional projectors (>12mm) and synchronous with film
motion.
Equipment is about to be set up to study and demonstrate the method.
No reference applicable to image reversal by the described method has
been found yet. An article by R Thaale and H. McGhee, "The Application o
----???????1111?111.11.1.."
Negative Feedback to Flying Spot Seanners" Journal British JRE, June 1952,
325-339 analyzes feedback systems for the purpose of gamma correction and
screen afterglow compensation.
JB/ls
STAT
14
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LI
io
L.9
7
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Lc) k.,
Limitations of Electroluminiscent Displays
Ordinary television practice requires a signal to noise ratio of at least 35 DB.
40 DB is considered
======
able. Systems which reproduce photograpla-by electronic means are sub-iect-to
noise influence particularly because of the decay rates of phosphors when applied
to scanning systems. The information content of a photograph requires band widths
as high as 1500 megacycles for reproduction equivalent to that of a single optical
system. The following calculation shows what can be expected of systems of this
type.
excellent but S/N ratios less than 30 DB are totally unaccept-
16
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THE PICK-UP OF FILM FOR DISPLAY OVER TIEB TELEVISION
SYSTEM, A SURVEY OF TECHNIQUES
INTRODUCTION
To view negative films as positive, using mere physical means rather than
to proceed through a photographic process, seems to be advantageous in cases
where rapidity of access is important. To use television techniques for this
objective seems obvious. It is relatively simple to produce any reasonable
transfer function with electronic means, inverting tone values and shaping gra-
dation curves at will. The main problem is that of television film pick-up.
The feasibility of an inexpensive system will greatly depend upon the choice
of the system.
OUTLINE OF THE PROBLEM
The major difficulty of displaying conventional films over the television
system arises from the fact that both techniques have standardized to a different
frame repetition rate. Commercial films are run at a speed of 24 frames/sec.;
amateurs usually use 16 frames/sec., whereas television technique has adopted
in this country a repetition rate of 30 frames/sec., interlaced 2 to 19 or 60
half-frames/sec.
Many difficulties would be eliminated if special films comprising 60,framesi
sec. were used for example. The cost of operation need not be higher than with
24 images/sec. as an anamorphosis producing a corresponding compression-of the
picture height could still result in an acceptable resolution. Unfortunately
17
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?4.01
this is not a current practice, so television engineers had to use their invent-
ive strength for finding their way out of the difficulty.
CLASSIFICATION OF THE FILM PICK-UP SYSTEMS
Depending on whether one considers it practical to depart from conventional
techniques either for film or for television for special applications, four com-
binations are possible:
1. Standard motion-picture film in conjunction with the conventional
television system as for broadcast use;
2. Film of unconventional standard specially produced for television
display;
3. A modified television system, suitable for closed circuit tele-
vision using simplified design;
4. The fourth combination with both unconventional film and tele-
vision system does not seem to add a practical advantage.
A classification of the three first-named combinations with subdivision
of a variety of pick-up systems are listed in Figure 1. Only the first combi-
nation is used commercially.
mcgraquEs USED IN BROADCAST TELEVISION
A. Flying Spot Scanners for Still Pictures
The principle of the set-up used for a still picture is shown in '
Figure 2. The television raster is written on the screen of a flying spot
tube (1) which uses a phosphor having a very rapid light decay. A lens (2)
1
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Film Pick-up Systems
Standard Film
Conventional TV
Continuous
Film Motion
Intermittent
Film Motion
[JFlying Spot II
-
Scanners
I
.0-1Electronic
Compensation
Optical
Compensation
Fast Cycling
Projectors
Pick-up Tube with Mamory,
Movie Projector
Iconos cope
Vidicon I
Unconventional Film
Conventional TV
60 Frames/sec Film
Anamorphotic
Pictures
Unperf. Film
Electro-optical Synchr.
Flying Spot Scanner,
Continuous Film Motion
FIGURE 1
Standard Film
Unconventional TV
egainewees
Increased Blanking
Time
1.--X.
Movie Projector
Fl ing Spot Scanner
Single CRT,
Feedback System
-1
Unconventional
Scanning
Sine Wave
Spiral
Low Frequency
High Resolution
Velocity Modulation
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projects the raster on the transparency (3) and a condenser (4) collects the
transmitted light which falls on a photocell of the multiplier type (5).
The picture quality obtainable is high. The limit of resolution
using conventional components can exceed the limit of the television system.
There is a fair relationship between signal amplitude and the transparency of
the slide and the light transfer characteristics need little to be corrected.
Signal-to-noise ratio of the video signal is high for transparency of not too
high density (D< 2).
B. Flying Spot Scanners with Electronic Compensation
The pick-up of film adds a kinematic problem because of the different
repetition rates and the very short blanking time of the television system. One
approach to the problem involves a flying-spot scanning system and continuous film
motion. The raster on the flying spot tube is displaced vertically in a sequence
of 5 distinct levels by adding a composite step signal to the conventional ver-
tical saw-tooth scan. One film frame is scanned three times, the next frame twice,
the following three times again, thus producing the average ratio of 5:2.
Although this system seems very simple it is almost impossible to
achieve the required accuracy of a fraction of a line for all 5-scans over the
entire picture, as well as an even distribution of light. For a frame rate of
16 images/sec., with the required ratio of 4:1, the difficulties would be even
greater.
C. Flying Spot Scanners Using Optical Compensation
Here the geometrical correlation between the continuously moving film
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kftd ,d017
FIGURE 2
2
LI
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and the scan is performed by optical means. The optical elements most used
for performing this compensation are either rotating And tilting mirrors or
rotating glass polygonal prisms. These optical elements follow the film move-
ment in such a way as to produce a virtually immobilized image of the film
frame in its conjugate plane. Many different systems have been proposed and
built but only very few have reached the market. This is perhaps illustrative
of the difficulties encountered.
In order to produce a high picture quality without noticeable jumps
between image change-over and without flicker, it is necessary to apply un-
usually high mechanical precision and a rather expensive set-up. As with elec-
tronic compensation, a film shrinkage correction is required.
D. Fast Cycling Systems
As mentioned above the blanking period of the television standard
is much shorter than the cycling or pull-down times of conventional film pro-
jectors. The blanking period Comprises 13 television lines or 0.83 meg. com-
pared with some 15 msec. for current projectors.
Some projectors have been designed for moving the film in a time
comparable with the blanking period, taking care not to exceed the tensile
strength of the film base. The severe problems encountered here are those of
excessive wear of the mechanist as well as the film itself and high noise level.
E. Systems Using Pick-up Tubes with Storage Characteristics
The progress made on vidicon pick-up tubes has enabled one to build
very simple and efficient television film scanners. These are, in fact, the
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Q.)
most used type for film pick-up today, and most manufacturers have ceased to
produce flying-spot film scanners as well as pick-up projectors using iconoscopes.
In principle) the set-up involves a movie projector and a vidicon cam
mere. The image projected on the photoconductive layer of the vidicon produces
a pattern of conductivity which decays slowly with time. The image can thus
be scanned several times without significant loss in signal amplitude.
The image quality compares quite favorably with that delivered by
the before-mentioned systems, especially with respect to lack of flicker and
jitter. The resolution produced by the vidicon is comparable with that of
regular 16 mm film and is slightly less than that obtainable with still picture
flying-spot scanners. The possibility of aperture response correction (restor-
ation of full level for high picture frequencies) is particularly' inviting be-
cause of the high signal-to-noise ratio. Of course, only an increase of the
horizontal resolution is practical, although methods for vertical aperture cor-
rection have been proposed.
NON-CONVENTIONAL SYSTEMS
For some purposes different from pick-up of motion picture films for broad-
cast transmission, there is no compulsion to stick to established standards.
Some variations seem able to simplify the problem tremendously. As mentioned
in the introduction, film specially designed for television transmission with
60 frames/sec. would greatly simplify the design of flying-spot Scanners while
replacing film perforation by optical synchronization marks may result in a
better utilization of the sensitive surface.
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A substantial increase of television frame blanking time enables one to use
regular film cycling mechanisms together With flying-spot techniques to make a
relatively simple setup. To compensate for the decreased time left for trans-
mitting picture information, a higher line scanning and frame rate and thus a
higher frequency limit is dictated.
One system which seems particularly suited for negative-positive conver-
sion is the
? SINGLE CRT FEEDBACK SYSTEM
Fig. 3 shows the principle of operation.(1) is a flying-spot tube whose
raster is projected through lens (3) on to the negative (4). The condenser (5)
collects the transmitted light on the photomultiplier (6) as for a regular fly-
ing spot scanner. A feedback amplifier (7) works in the direction of increasing
the luminosity of the cathode-ray tube in proportion to the amount of light ab-
sorbed by the negative for every picture element. The result is a positive dis-
played at the flying-spot tube itself which can be viewed, e.g., through a semi-
transparent mirror by an observer (9).
The necessary amplification is roughly estimated in the following calcula-
tion. Assume that a change of 5V at the grid of the flying-spot tube is neces-
sary to produce a change in luminous flux emitted from the screen of 0.5 lumen.
If the lens f number is 4, the highest useful negative density of 2.3 (trans-
mittance) 0.005., the magnification of the imaging system 0.08, the light
efficiency of the system 0.1, the luminous sensitivity of a typical photomultiplier
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tube (1P21) 50 A/lm and the load resistor 500-0.1 the output voltage at this
resistor is
0.5 x 0.005 x 0.08 x 0.1 x 50 x 500
= 0.78 10-2V
4 x4 x4
and the required amplification is thus approximately 650.
With a scanning system of Increased blanking time the tone inversion of
film seems easily achieved with the film cycling mechanism of a regular movie
projectors.
One limitation over a two-tube system is that there is no way to increase
the gamma above 1. One more severe drawback is produced by the blue, color of
the viewed picture (all short decay phosphors are blue) which makes it difficult
to judge the tone value.
One way of overcoming this limitation is by making use of a more complex
CRT. Fig. 4 shows a setup with a special scanning-spot tube (1) comprising a
double layer phosphor (2). The inner coating is a short decay) blue phosphor-
escence-type phosphor of the P16 type. The outer coating is of a color close
to white with a decay time of a few tenths of a second. Through the optically
flat glass plate (3) and the mirror (4), the raster is imaged in the usual way
on the negative. The blue sensitive photocell (8) reacts to the transmitted
? -light and) together with the amplifier (9) controls the luminosity of the CRT.
The negative pattern produced can be viewed at (10). The white phosphor is
excited either by electron bombardment or by fluorescence from the blue light
of the P16-type phosphor or by both radiations. The electron gun and the optical
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10
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L.)
axis going through the phosphor layers depart slightly from 900 as both are on
the same side of the screen. The advantage of such a system over the before
mentioned inverse feedback system is to produce a white picture with a smaller
flicker effect, as the white phosphor for visual display need not be of extremely
short decay. A suitable CRT is presently not available commercially.
OTHER METHODS OF TONE INVERSION, NOT USING SCANNING TECHNIQUES
One method not correlated with TV techniques makes use of the effect known
as phosphor quenching. A phosphor layer is equally irradiated with ultraviolet
light and emits visible light. A negative is projected on this layer with red
or infrared light of high intensity. As radiations of long wavelength will in-
hibit the fluorescence. of some phosphors, a positive image is made visible.
An apparatus using this effect is produced by Meteor, Siezen? Westfalen,
Germany and sold under the name of "Vertoscope" by C. P. Goers, American Optical
Company. It is suitable for still pictures only.
As a different approach to the problem, it may be possible to use the sub-
traction of light energy by utilizing coherent light, with a kind of interfero-
meter setup. One severe problem may arise from the fact that photographic
transparencies are not of truly equal thickness.
A further method to produce negative tone rendition for still pictures may
be to use reversible chemical color reactions initiated by light. of specific
wavelength and destroyed by different wavelength. Several dyes formed by ultra-
violet light and bleached by red light are known.
..111:mk
STAT
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C.)
BIBLIOGRAPHY
V. K. ZwOrykin, G. A., Morton, "Television", John Wiley, New York, 1959.
Donald G. Fink, "Television Engineering", McGraw-Hill, New York, 1952.
Victor Graziano, Kurt Schlesinger, "Continuous All-Electronic Scanner for 16mm
Color Motion-Picture Film", Journal SMITE, Vol. 62, pp. 294-305, April 1959.
A. C. Jensen, "Film Scanner for Television Transmission Tests", Proc. IRE,
Vol. 29, pp. 243-249, May, 1941.
A. G. Jensen, R. E. Graham, C. F. Mattke, "Continuous Motion Picture Projector
for Use in Television Film Scanning", Journal SMITE, Vol. 58, pp. 1-21, Jan-
uary 1952.
E. H. Traub, "New 35mm Television Film Scanner", Journal SMPTE? Vol. 62, pp 45-
54, January 1954.
Otto Wittel, "A Continuous Projector for TV", Journal SMPTE0 Vol. 69, pp 319-
3210 June 1955.
Otto Wittell Donald G. Haefele, "Continuous Projector Problems", Journal SMPTE0
Vol 69, pp 321-323, June 1955.
Warren R. Isom, "Fast Cycling Intermittent for 16mm Film'', Journal SMITE, Vol
62, pp 55-63, January 1954,
Ralph V. Little Jr., "Film Projectors for Television", Journal SMITE, Vol. 48,
pp 93-110, February 1947.
Raymond W. Wengel, "Pneumatic Pulldown 16mm Projector", Journal SMITE, Vol. 62,
pp 385-390, May 1959.
W. E. Stewart, "New Professional Television Projector", (RCA TP-6A), Journal
SMITE, Vol. 62, pp 390-399, April 1953.
R. G. Neuhauser, "Vidicon for Film Pick-up", Journal SMITE, Vol 62, pp 142-152,
February 1954.
Henry N. Kozanowski, "Vidicon Film-Reproduction Cameras", Journal SMPTE Vol.
621 pp 153-1620 February 1959.
M. H. Diehl, "A Transistorized Vidicon Camera for Industrial Use", Journal
SMPTE, Vol. 69, pp 795-800, November 1960.
C. L. Townsend, E. D. Goodale, "The Orthogram Amplifier", RCA Rev., Vol XI,
pp 399-410, September 1950.
28
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Signal to noise ratio of output of flying-spot scanner, considering
only shot noise of photo current and effect of luminescence decay of phos-
phor for practical example.
Energy impinging on screen of typical flying-spot
CRT: 27 kv x 150 uA :
4,05w
Conversion efficiency of P-16 phosphor
:
8%
Light (UV) flux emitted
:
0.32W
Light gathering efficiency of optical system
for a lens aperture of F/2
:
0.062
Light flux reaching photocathode through film
of density 0.3 (transmission 0.48)
0.32 x 0.062 x 0.48
:
0.95 x
10-2 W
Sensitivity of photo-cathode of 1P21
photomultiplier for spectral emission of
P-16 phosphor
:
30 mA/W
Photo current I : 0.95 x 10-2 x 30 x 10-3
=
28.5 x
10-5 A
Shot noise Ir = V2oe-I-4f
Signal to noise ratio S = ? 1
V 2e v f
,\/28.5 x 10-5 A 1 . -V8.9 x 1014 . 3x107. 1
2x1.6x10-19Cb
Signal loss due to value of luminescence decay for P-16 phosphor:
for 3 Mc bandwidth, signal decreased to 0.93 (luminescence decay to
7% after 0.15 us)
10 Mc
30 Mc
100 Mc
0.75
0.40
0.08 (extrapolated value)
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? L...=)
S/N for 3 Mc = 3 x 107 x 0.93 = 16000 or 42 db
1.73 x 103
3 x 107 x 0.75
10 Mc = = 6800 or 38 db
3.3 x 103
30 Mc = 3 x 107 x 0.4 = 2200 or 33 db
5.5 x 103
100 Mc =
3 x 107 x.08 = 240 or 24 db
104
Quality limitation of flying-spot display
Resolution
Scanning raster, bandwidth, spot size of scanning and display CRT due
to beam diameter and light scatter in phosphor persistance :i optical aber-
rations.
Noise
Phosphor granularity, photo multiplier noise (mainly photoelectric
shot noise, also noise from thermionic emission of photo cathode and elec-
tron multiplier) amplifier noise.
??? Nr.
) 6 r
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OVA- istaiiinaton, Lmmj
To:
Subject:
INTEROFFICE CORRESPONDENCE
Optical-electronic Display System Date: 13 January 1965
CC:
File
The diagram shows a proposed projection system which incorporates a
variable edge-gradient enhancement feature. It is a two-stage system,
with a cathode-ray tube screen at the intermediate image position.
The picture to be viewed Is. contact-printed (e.g. continuous tone
diazo, for preservation fine detail) to a high contrast--too high for
direct projection. The Terifit is placed in the projector gate, on left of
the TV tube. A field lens is also used her so that the light enters a
second projection lens beyond the TV tube and is projected on the screen.
STAT
STAT
STAT
The TV tube adds an electronic image at the intermediate image posi-
tion. (It is possible that the combination could be viewed directly, but
the second stage of the projection system is shown for completeness.) The
electronic image is obtained by scanning the original negative, or a print
from it. It is of low contrast, negative and unsharp. When it is added to
the high contrast positive image, it has the effect of reducing the gross
contrast to a contrast which is more suitable for viewing. However, be-
cause this negative image is unsharp, the contrast of the fine detail in
the composite image is not reduced, and so fine detail appears enhanced
in contrast by comparison. Control of the contrast of the negative image
gives a degree of control of the apparent fine detail contrast in the
composite image.
JELT:mic
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EXMA-HIGH CONTRAST
POSITIVE
NON-ACTINIC FILTER
441
(CONDENSER NOT SHOWN)
LOW-CONTRAST
UNSHARP TV IMAGE
TRANSPARENT
PHOSPHOR
?
?
SUN
SIGNAL FROM
SCANNED NEGATIVE
OPTICAL PROJECTOR WITH ELECTRONIC EDGE ENHANCEMENT
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? ?
Swept Laser With Feedback for Contrast and Brightness Control
AMPLIFIEl<
X AXIS
ANALYZER DEFLECTION
\GAS LASER/ 12Z-D4
KERR ELECTRO LENS
OPTICAL SHUTTER
PHOTOCELL
DIFFUSER -----
FILM
SCREEN
BEAM
Y.AXIS
DEFLECTION SPLITTER
Contrast and intensity range .of a projected image may be controlled using a
scheme such as that shown in Figure As shown, a gas laser produces a beam
of plane polarized light. The beam passes through a Kerr Electro-optical shutter
to an analyzer which is set to transmit the unrotated plane polarized light. The
beam then passes through a lens which is brought to a focus at the screen. On
the way it passes through X and Y axis deflection birefringent crystals for X
and Y scanning of the beam across the screen. It also passes through a beam
splitter which extracts a portion of the light which is focused on the film to
be projected.
Light passes through the film, ?as the beam is deflected, is partially absorbed
by image detail and reaches the photocell after being diffused at the diffuser.
The photocell output is thereby amplitude modulated and after amplification
applies feedback control to the laser beam intensity by means of the Kerr shutter.
By appropriately varying the gain of the amplifier both absolute brightness and
contrast may be controlled.
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BANDWIDTH LIMITED OPTICAL SYSTEMS
Zoom lens technology and aspheric lens design is discussed here. The testing
of the lenses by means of Optical Transfer Function testing is recommended.
These films are to be examined for their best application after determination
of the best projection method is established since enough is known about their
capabilities.
Scanned Systems are devised with the means for scanning.
33a
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PRESENT PROBLEMS AND DESIRED PARAMETERS FOR VIEWING
We should remember that the basic requirement is for maximum information
transfer in a minimum possible time to an observer from a filmed object. In
particular we must concern ourselves at present with the mechanical restric-
tions as now known. These restrictions must confine us to considerations of
information transfer from 9-1/2, 5, or 2-1/4 inch film onto a screen, as an
intermediate step, for observation by one or several viewers. In a flow
chart, the information transfer thus follows the following path:
Object being observed Film record Screen Observer
It has apparently been determined that a screen of the approximate size of
30" x 30" best fulfills present purposes, that viewing in normal room illumi-
nation is highly desirable, and that a capability of reaching 50 to 70 foot
lamberts is necessary. Resolutions of 400 lines per millimeter at the film
plane is a requirement. It must be pointed out as discussed in "Methods of
Engineering Photographic Systems" by Geirge C. Higgins, Applied Optics,
January 1964, Volume 3, Number 1, that high resolution and high contrast are
not necessarily related. In viewing systems it is at least as important to
keep both resolution and contrast at a maximum in order to impart information
to an observer being focused by the lens not contributing to the image core
be removed from the image to enhance contrast, even to the degradation of light
levels.
It is desired to be able to rapidly scan photographs to find areas of interest,
to then observe these areas more closely at high resolution and magnification
under optimized conditions. Optimization techniques may include changing
roam illumination, varying image intensity, increasing contrast, or digitally
analyzing the image. These techniques may or may not be independent of each
other and will to some degree determine final optical requirements.
34
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A REVIEW OF THE PRESENT APPROACH TO THE PROBLEM
It was previously decided to limit present considerations to a fixed magnifi-
cation lens for enlargement of 2-1/4 x 2-1/4 film to 30 x 30 inch screen.
Because of the characteristics of the screen materials, color correction of
the lens was limited to 3650-4050 angstroms. Later attempts to modify this
lens to accommodate other formats by interchanging elements were unsuccessful,
partially due to the double-Gaussian form used. It had been concluded that
design at that time that the design of a fixed focus lens should precede the
design of a ultraviolet zoom lens.
The present projection system utilize: a 2500 watt mercury short arc lamp. By
means of a primary and secondary mirror in combination with a heat reflecting
filter, dichroics, and coated elements about 3% of the energy is transferred
to the screen. The percent lens design is an 8 inch f/2.8 lens with a dif-
fraction limited aerial image on axis and approximately 200 lines per millimeter
5 degrees off axis. The double-Gauss form was used because of its inherent
symmetry and consequent ease of correction due to cancellation of aberrations
between halves. It unfortunately also has inherent problems of tangential and
radical oblique spherical aberrations that degrade off-axis resolution unless
vignetted or corrected by aspherics. It is our present desire to first check
the lens when finally assembled by vignetting these aberrations. This will
quickly tell us what the aberrations are doing to resolution, contrast, and
illumination. We will then conclude on aspherization. It is often the case '
that aspherizing improves contrast of images while actually degrading resolu-
tion. It is thus extremely important that the matter be carefully studied.
35
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L.,=)
POSSIBLE APPROACHES BASED ON ABOVE CONSIDERATIONS
The above requirements indicate some method of changing format and magnifica-
tion. Suggested are magnifications of:
a. 13 x (2 1/4 x 2 1/4 to 30 x 30)
b. 6 x (5 x 5 to 30 x 30)
3 x (9 1/2 x 9 1/2 to 30 x 30)
Reviewing would be accomplished by reviewing the 9 1/2 inch film at 3 x
magnifications. When areas of interest pre found, a change of magnification
to 6 x or 13 x and the consequent decrease in format area could be accom-
plished. These magnifications would be campatable with other film sizes also.
General approaches to this could be:
a. A zoom lens corrected for magnifications of 13, 6, and 3 x and
continuously variable.
Variable magnification at 3 discreet magnifications by the replace-
ment of part or all of the elements by a turret or similar arrangement.
c. Multiple presentation of images on 3 separate screens by 3 separate
lens systems.
ZOOM LENS
A most simple mechanical solution to the variable magnification - variable
format problem would be a zoom lens. Optical design solutions to zoom lenses
require simultaneous solutions to the lens equations for different magnifica-
tions. Thus instead of solving to minimize (neglecting chromatic aberrations)
the 4 third order aberrations (neglecting higher order!) we must now solve
for 4 x 3 or 12 conditions.
36
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C=mj
It is in practice found that, although in theory, the twelve simultaneous
solutions may be solved, no practical solution always exists when constraints
on glass thickness, index, ahromatic corrections, and higher order aberrations
are added. The design thus in practice becomes a compromise at 3 points.
It is conceded that it is possible to use the basic zoom lens types and design
for a high state of correction at one particular format, while settling for
more mediocre solutions at other magnifications. It is suggested that a more
detailed study should be given to the design of a high resolution, zoom lens
of our requirements. On the surface, this approack appears of sufficient
difficulty to study carefully all alternate approaches.
TURRET APPROACH TO OPTICAL DESIGN
The design of a variable magnification lens by use of interchangeable components
is well-known. Generally, this amounts to a stationary positive group with
wide-angle, normal, and telephoto attachments. Variations may include more
general replacement of elements.
Going one step further, it would be possible to use three distinct lenses (one
for each format). This suggests, however, perhaps an unique approach.
MULTIPLE PRESENTATION
Using three lenses it would be possible to present, simultaneously on three
separate screens, three images. A simple design would include dichroic
beam-splitters to separate spectral components. These components would then
be focused by different lenses and directed to screens. A possible layout is
illustrated on the following page.
The advantage of this approach is immediately obvious. Presently, dichroic
beam-splitters are being used to separate out the ultraviolet energy for
37
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projection onto the phosphorescent screen. This method would not cut the
ultraviolet radiation levels but would make efficient use of the other light
already available and not being used. It would furthermore allow simultaneous
examination of areas without changing the scanning format, allowing a comparison
at two magnifications.
Each lens could have a narrow spectral correction and could possibly be
purchased off the shelf, eliminating the necessity of lens design or at least
allowing test of the system without awaiting a lens.
38
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1 g
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LENS COATING
New high efficiency loatings (HEA Multilayer) are providing up to 95% trans-
mission capability in the ultravoilet and visible regions. It is proposed
that these coatings be used not only in the lens elements but also on the screen
face to eliminate room reflections. One of primary interests SI-AT
lies in the production of multilayer coatings. The following discussion
originates from the person who was primarily concerned with the computer
programming and development of techniques for making both HEA coatings and
dichroic filters.
THE OPTICAL TRANSFER FUNCTION
The bearing of the Modulation Transfer Function upon low contrast photography is
related to the ability to obtain as high a resolution as possible. In evaluation
of improving the visual recognition of images is yet to be determined in terms
of the MTF. This MTF enables the lens designer to judge what changes are
necessary to improve the lens. If for example, the film is the limiting factor
in the overall MTF, then it is futile to continue attempting to improve the
lens design. In this particular situation it becomes necessary to find a more
suitable film.
Th 34
The optical transfer function (OTF) has been introduced as an optical analyses
technique over the last ten years. The concept of an optical transfer function
is an extension from the electrical engineering communication theory and many
of the same concepts are applicable.
Basically, the OTF is the result of employing a Fourier Intergral to obtain the
properties of the optical image. The integral can be employed for the target,
the lens system, and for the film upon which the image is recorded. Once the
OTF has been obtained for one component of the total optical system, the over-
all recorded image quality can be obtained.
40
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Declassified in Part - Sanitized Copy Approved for Release 2012/09/11: CIA-RDP79B00873A001600010003-4
-wx
The Fourier Integral is given below. The term ej is known as the Kernal
Function. By performing this integration, the components of f(x) can be
obtained. Essentially, we then obtain the frequency components of the in-
tegrand f(x). The complete integration will result in components which have
some magnitude as well as phase. For this discussion it is only necessary to
consider the amplitude at each spectra or frequency.
F(w) =
co
wx
f f(x) eTdx Fourier Integral
co
In general, this integration is a complex integration process and rather
difficult to compute by manual methods. However, high speed digital computers
have reduced the amount of effort necessary to evaluate such integrals.
In order to analyze the system, it is only necessary to determine the amplitude
of the OFT. This amplitude is called the Modulation Transfer Function (MTF).
The MTF is a normalized amplitude, which is obtained by dividing the amplitude
at any particular frequency by the value of the amplitude at zero frequency. An
MTF can be established for several parts of the system independently or together.
By multiplying the several MTF's together, the total amplitude of the MTF through
the complete system can be calculated to evaluate the overall system.
The MTF of the film and lens system might be linear, but the screen MTF may not
be linear. The problem in this case is to determine several film MP's of
various lighting conditions for the film type and the method of developing
the film.
The optical transfer function permits both the designer and the user to judge
uhat portion of the projection process that improvements should and can be
made.
41
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DETERMINATION OF THE MODULATION TRANSFER FUNCTION
?Various methods are presently available to determine the MTF. Some of these
methods are the active type employing rotating lenses, prisms, etc. These
active devices possess vibration problems which limit their use. The more
generally employed method at the present is the use of a sinusoidally modulated
target. This target is made up of a series of repeating sine waves whose
density varies as the gine function. The more frequently this pattern repeats
itself, the greater its frequency. This sinusoidal target is imaged by the lens
system. Before the image reaches the image plane, it passes through a slit
parallel to the sine wave pattern. The slit permits scanning only along one
line. A film strip is utilized to record the impression as the target is
drawn past. This process is demonstrated in Figure B-1.
By observing the flourescent screen formed by this target and analyzing the
amplitude of the light, an MTF can be determined. The screen light intensity
can be read by means of a microdensitameter and by plotting the results from
the lowest to the highest frequency distinguished by the system. The output of
a lens system may also be read on a photamultiplier tube to analyze the output
light. A similar configuration of target lens system and scanning slit would
be used for the phototube method.
employs the most recently developed
photometric microscope and linear logarithmic photometer manufactured by Gamma
Scientific, MOD 700-10 and MOD 700. This instrument is capable of measuring
areas as small as 0.00015 inch:. indiameter with the proper eyepiece and fiber
optic photometric optical objective.
After performing the process of taking the picture of the target as shown in
Figure B-1 a set of curves will be obtained by reading the microdensitameter.
Its output will be a series of nearly sinusoidal waves expressed as a function
42
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Declassified in Part - Sanitized Copy Approved for Release 2012/09/11: CIA-RDP79B00873A001600010003-4
,
of the frequency of the target. As the frequency increases, the system becomes
less able to distinguish one sine wave from another as demonstrated by the re-
duction of the amplitude change of the density in Figure B-2 (a). The amplitude
at the lowest frequency is then selected as a normalizing value and the normal-
ized values of the amplitude ration can be plotted as shown in Figure B-2 (b).
43
t
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Declassified in Part - Sanitized Copy Approved for Release 2012/09/11: CIA-RDP79B00873A001600010003-4
Lir)
.-4
2 co
.J
LJ
LENS SYSTEM
pci a)
4
0
co)
0
4-)
4-1
44
C0
0
a)
H
4-1
ry.4
4-)
t.0
0
0
0
44
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Declassified in Part - Sanitized Copy Approved for Release 2012/09/11: CIA-RDP79B00873A001600010003-4
DENSITY
OF IMAGE
MFT
MODULATION
TRANSFER
FUNCTION
SET OF FREQUENCIES
(a)
SPACIAL FREQUENCY (LINE/mm)
(4)
FIGURE B-2
Reducing Data to Obtain the MTF
13-182
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THIN FILM TECHNOLOGY
Multiple layer optical coatings have been investigated by
since the World War II period. In recent years, efforts have
been devoted to developing mathematical solutions and computer programs
for designing multilayer coatings. Programs were developed for solving
the reflectivity and transmission of multilayer films with variations of
the following parameters: (1) number of layers (any number); (2) re-
fractive index; (3) thickness; and (4) wavelength.
Methods for calculating absorbing films, nonhomogeneous films and
variations with angle of incidence, have also been developed. Simplified
methods for vector analysis have been developed and suffice as guides
to exact computational research for new coating configurations.
Utilizing the theoretical approach, special coatings are investigated
by computer before experimentation. This investigation includes the
calculating of the progressive changes in reflectivity or transmission
as each layer is being deposited. The prediction of these changes in
reflectivity has also led to the development of monitoring devices for
the precise control of coating thicknesses. For some of the coatings
developed the monitoring equipment has been automated for production
purposes.
Extensive research has been conducted in developing evaporation
techniques and in studying the properties of numerous stable oxides such
as Ti021 A1203 SiO CeO2, and Le203, many fluorides such as CeF3and LaF3,
beside the commonly used materials such as M02, and ZnS. Investigations
STAT
STAT
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L.=?)
of refractory metals and many rare earth compounds have also been
performed. In addition, work has been done in evaporating metals such
as chrome-nickel alloys, chromium, gold, silver, aluminum, and copper
as transparent conducting films.
? The development of evaporation techniques and investigation of
materials has resulted in a selection of materials which has a variety
of indices, absorption coefficients, and environmental stabilities, and
are available for solving optical thin film problems.
Utilizing computer programs, materials technology, and monitoring
devices, we have developed coatings for antireflection systems, color
corrected (by use of thin films) lens systems, transparent conducting
films, and numerous neutral and dichroic beam splitters. Some of these
coatings were of the classical struction of 1/4, 1/2, etc., layer
thicknesses of the central wavelength. Other coatings, however, consisted
of layers which were not 1/4 wavelength or a multiple thereof in thickness.
47
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GAL ..AILitit 141-rh YiRY InG11 FREQUENCY CAPABILITY
The possibility of us5r1g a CW (injection) solid state laser as a
light source in a recording oscillosraph has brought within sight a
potential writing speed some 300 tiries that available with present-day
silver halide materials.
.Such a writing speed, of perhaps 1.5 x 107 inches per second, will
be quite useless unless a galvanometer is available capable of a
frequency response of the order of 5 megacycles. This is quite
.impossible with mechanical systems, which now go up to.13 kc and which
cannot be pushed much further, even if radically different configura-
tions are considered.
A virtually inertialess light. deflecting device might be made as
part of a laser cavity, in the manner to be described. However, the
reduction to.practice of such a ,device would be dependent on the
availability of a. suitable ultrasonic transducer for use in the thousands
of megacycles range, and with the necessary wide bandwidth.
\-- 2
I---N
\I !
, <
The other
reflected
tion grat
back into
radiation
Since the
expected
available
In the diagram, A is an injection
(solid state) laser cavity (plan view)
with a totally reflecting surface on the
left. B is a cell containing an ultra-
sonic modulating elementl. In this case
C.cle totally-reflecting surface on the 1
right of the light modulator completes
the laser cavity. A source of Kilo-
megacycle electrical energy is connected
to a transducer at one end of the cell.
?end should be such that the energy is absorbed rather than
The ultrasonic energy in the cell has the effect of a diffrac-
lag. While most of the radiation is reflected in the zero-order
the laser cavity, thus providing the required feedback, some
comes out at an angle on either side, mostly in the first 'order.
energy in the zero order is returned to the system, it may be
that the energy in one side beam will be close to SO% of the
output.
? The angle of diffraction will vary with the frequency of the ultra-
sonic output to the cell, as de.,cribad below. Hence, the beam will move
through an angle in the same way as a beam from a mirror galvanometer.
Deflection could be very much faster than is feasible with a system, such
as that of a mirror galvanomer, having mechanical inertia.
48
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?
Calculation of Grating Constant d
ft/
?A 4" (double-amplitude) deflection with 11" optical arm is usual for
a galvanometer in oscillograph recording. This is about 10?20' each side
of nozmal. We shall calculate the grating
constant for a diffracted angle of
45??10?20', i.e. 34?40',45? and 550201
< =.p for the first order.
where n (order) = 1
Assuming a wavelength of 6500 A = 6.5x10-5'cm,
-1
cm
1
d 6.5x105
Forp = 34?40?, 1 =
0.5688
=
0.875x104
am-1
d
e
6.5x10
For p 45?, 1 .
0.7071
.
1.088x104
cm-1
d
6.5x10-'5
For p = 55?20', 1 .
0.8224
=
1.265x104
cm71
d
6.5x10-5
In a similar calculation for the second order beam we find that for
60? deflection a reciprocal grating constant of 6.66x10"/ cm-1 would be..
required. At the grating constants calculated above, the second order !
/
would be diffracted more than 60?, so the second order beam would not :
/
overlap the range of the first order beam, and may be cut out by a suitable
mask.
Frequency of Ultrasonic Radiation
The velocity of sound in liquids and solids varies from 500 m/sec
for rather soft solids up to about 6000'm/sec. The lower the velocity,
the lower the frequency required for a given grating constant. The
frequencies will be calculated for water using a velocity-of 1460 m/sec.
= , or 'A = ? 3: ?
Where V = velocity of sound = 1.46x105cm/sec in water
*6 = frequency
= wavelength
At 34?40', = 0.875x104
At 45?
1=
At 55?20', 4. =
Declassified in Part - Sanitized Copy
1.088x104
1.265x104
Approved for
111-= 1.46x105 x 0
? 1.46X105 X 1
? 1.46x105 x 1
Release 2012/09/11
.875x104 = 1.278x109 sec-1
.088x104 = 1.588x109 sec4
.265x104 = 1.847x109 sec-1
: CIA-RDP79B00873A001600010003-4
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? The figures given are very approximate because no account has been
taken of dispersion; i.e., variation of velocity with frequency. A
substantial variation may have accrLed by the time these IC frequencies
are reached.
As regards the problem of generating ultrasonic radiation in the
kilomegacycle range, the newly developed depletion layer transducers
appear to be promising. 2 These devices function in the desired frequency
range. Furthermore, their resonant frequency may be varied by a d.c.
bias. They may be made from such materials as gallium arsenide or
cadmium sulfide.
Response Time
If the frequency with which the transducer is excited is abruptly
changed, this change will be propagated along the cell, across the laser
beam. While the change is in transit, pat of the beam will be diffracted
at the old angle and part at the new. Hence the transit time across the
beam is of interest.
Typically, a beam fronithe kind of laser under consideration would
be .004" = .210 cm wide. At a velocity of 1.46x105 cm/sec, transit
time = 10- = 68.5x10-9 sec.
1.46x1V
Since we spoke earlier of a frequency response of 5 megacycles, It
is of interest to see what this response time amounts to in terms of a
phase angle at 5 megacycles. Duration of 1 cycle at 5 me = 200x109 sec.
Phase angle = 68.5 x360 = 124?
200
At 1 mc, phase angle = 250
While this does not look too encouraging on paper, it should be
remembered that high frequency response is normally required for record-
ing rapid changes in the quantity being measured; and when the recording
beam is in rapid motion across the paper, the fact that it has a "tail"
may not be of great importance. The effect may be minimized by using a
material in the light modulating cell in which the ultrasonic velocity is
much higher. in practice it could be about four times higher than in the
example given. But to produce the same grating constant a higher ultra-
sonic frequency has to be used in the same ratio as the velocity of its
50
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propagation. For example, if a?medium were chosen in which the velocity
were 6000 m/sec., the frequencies raquired would be 6000 or 4.1 times
1460
those calculated for a water cell; that is, about 5 tO'7x109-sec-1, The '
phase lag at 1 mc would then amount to 6?.
1. G. W. Willard, J. Acoust. Soc. Amer. 21, 101 (1949)
2. "Depletion Layer Transducer - a New High Frequency Ultrasonic
Transducer," by Donald L. White of Bell Telephone Labs,
1961 I.R.E. International Convention Record, Part 6, p. 304.
51
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STAT
F25-7
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Lr)
COMPUTER INTERFACE DISPLAYS
? Associated with the problem of storage and processing information is the display
of the information for human observation. The historical method has been-to
sweep the display horizontally one line at a time similar to television. This
method could also be applied in presentation of digital information on a cathode
ray tube. The ordinary T.V. (21") with 535 lines represents approximately 25
lines per inch or 1 line/mm. This is a relatively coarse picture as far as
resolution is concerned.
Now it would appear that the CRT offers a more versatile method of presentation
than is normally done. That is, with the proper controls on the CRT including
Z-modulation (brilliance) it is possible to draw lines of any length and at any
angle starting at any particular point. Perhaps several lines could be drawn
parallel to widen lines without "blasting the phospher" with high electron beam
intensity. Care should also be taken to assure that a sufficiently small spot
be utilized.
Another possibility is to employ printers to actually print maps. In the case
? of printers, it would be more beneficial for the machine to print one line of
output at a time.
If an X-Y plotter were used, the various lines, axes or dots could be made
although the settling time for an electro-mechanical system would require an
inordinately large time to print a bit of information contained in one dot
compared with the time to draw a straight line.
52
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ci
The various aspects of CRT's versus printers versus plotters would have to be
analyzed in the light of specific requirements.
SUMMARY
Cathode Ray Tubes would be the most practical system to be employed for rapid
visual presentation. A one-line-at-a-time printer could be employed to stamp
out digits. In the case of an X-Y plotter, it may prove more beneficial in
essentially drawing one line at a time to result in a faster production of a
display with a minimum requirement for storage of information. Various other
display devices will be examined to evaluate their usefulness for this purpose.
MAP Display
Presentation of a map will require just two states of amplitude information.
That is whether there is a light or a dark area. This as a picture (map) is
scanned in a series of digits picked up which can represent the picture. Let
our format be divided up into a dimension X by Y millimeters. If these
dimensions are to have a resolution of amspotes per millimeter then across one
dimension say X we should have a total of oc.X spots. Allowing two states of
amplitude we should get 2..X.X spots in one trip across X. Now in order to
cover the Y dimension, we have to give the same resolution factor to Y as we
did to X with the result that the total number of sweeps is oLY.
?A total information count can be calculated by 2.*2-X-Y. The process of
information storage becomes quite large if we consider X & Y to be 50 mm each,
and otto be say 100 lines per mm. Hence, the total can be calculated to be
2 x 1002 x 50 x 50 = 5 x 107 bits.
The IBM 1620 computer has a capacity of 4000 words which are in decimal form.
Since a decimal equivalent storage expressed in binary is 120,000 bits, it
53
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Declassified in Part - Sanitized Copy Approved for Release 2012/09/11: CIA-RDP79B00873A001600010003-4
Las=1
would require 5 x 107/1.2 x 105 or 41-1/2 IBM 1620 computers to store all the
information (on a black and white basis) in the map. Were we to permit shades
of gray (say 10 different shades) the overall requirement then becomes 5-107-10
9
or 5 x 10 bits. Needless to say this represents a very large amount of
information.
Two alternatives are available to us: either increase the storage capacity of
the computer or decrease the stored information on the map at least on the
basis that we have assumed for representing this map. It may prove more
advantageous to store different types of information which may be various
types of short line segments or other types of geometric figures, like crosses
or circles. What is required is a review of information theory in regards to
character representation. Perhaps this review of information theory should be
tempered by what physical elements are available to both identify and print
our (or display) the character before going into too thorough a study. It
would be well to make such a review to better adapt the available machines to the
problem at hand.
SUMMARY
Perform a review of information theory to reduce the storage requirements for
representing the map. This review should take into account the devices which
would perform the extraction of information from some original map to the
devices which would perform the display of the map. It might well prove that
the best way to draw a map is not a simple dot drawing but a series of short
lines (or even continuous lines) might prove more beneficial than the dot
system'.
54
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Declassified in Part - Sanitized Copy Approved for Release 2012/09/11: CIA-RDP79B00873A001600010003-4
)
IMAGE ENHANCEMENT
Thoughts on Image Enhancement with FB Techniques
Feedback Theory
In general, a normal feedback system tends to employ proportional signals to
cause output to follow input. This is the general negative feedback employed
in many systems. However, there is a useful purpose in the use of positive
feedback. If a photocell output were fed back to modulate a light source, a
control of intensity could result. For instance, during scanning it would be
possible to increase at a relatively low density portion of the image and
decrease intensity at a relatively high density portion of the screen. This
scheme would work like a "volume-expander" in an audio amplifier. The result
should improve contrast in a low contrast photograph. However, since the
process really represents positive feedback, some care must be observed in
building such a feedback network. This technique is only possible on a
scanner system (an active system) where the illuminated spot is small.
The technique is not necessarily limited to U.V. but could also be utilized
with any light. It would work better with U.V. than visible light because of
ultra violet's shorter wave length.
A beam splitter could be employed to "pull off" some of the light after it had
passed through the transparency. A modulation of light source intensity could
then be made. It may be necessary to slow down the sweep to give the feedback
55
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Declassified in Part - Sanitized Copy Approved for Release 2012/09/11: CIA-RDP79B00873A001600010003-4
mechanism some time to stabilize at the correct amplitude. The fall-off at
end of the margins of the format (Cos 4 Law) could also be corrected by
attempting to bring the average intensity back to a normalized value.
It might also be possible to increase the intensity of the image in high
resolution points by use of lead networks. The problem here might be the phase
shift of the high resolution points. That is, an apparent shift in intensity
location might occur, but as long as the film is swept in the same direction
the image properties should be preserved.
CONTINUOUS
LASER
LIGHT
OUTPUT
CONTROL
MPLIFIER
FRESNEL
LENS
BEAM-SPLITTER
SCREEN
FILM
Physical Setup
COLLECTOR LENS
'PHOTO CELL
56
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Declassified in Part - Sanitized Copy Approved for Release 2012/09/11: CIA-RDP79B00873A001600010003-4
LAJ
SYSTEMS FOR SWEEPING/SCANNING
A pattern for scanning is important to establish the overall objects of drawing
maps versus detailed pictures versus character presentation. If it is known
that what is being scanned is binary then at some point in space (or time)
then a simple binary bit can be reproduced.
One can consider various mechanical systems such as rotating lenses, perhaps
even moving a laser at various angles would permit a scan to be made. The
lightest system would inherently possess the lowest inertia and would have the
highest response.
This lightest system is a mirror or galvanometer used in
oscillographs. However, even the best response of galvanometers is in the order
of 15 kilocycles.
Now to briefly examine the requirements of sweeping. If an assumption of 100
lines/mm resolution is made and a format of 25 mm high is taken, then the
number of sweeps to be made is 2500 lines. Furthermore, if a sweep is to be
made in 1/30 second then a capability of 75 kilocycles is necessary assuming
a fast "fly back." If an assumption is made where a sine wave is to be
employed, then since a sine wave sweeps up across and back in one cycle, then
only half the rate or 37 kilocycle response is required.
Now the requirement for 100 lines/mm over a 9 inch format is much greater. The
basic requirement in cycles per second is
100 x 9 x 25 x 30 or 675 kilocycles
57
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Declassified in Part - Sanitized Copy Approved for Release 2012/09/11: CIA-RDP79B00873A001600010003-4
for a saw-tooth wave form and only 338 kilocycles for a sine wave trace. The
actual capability requirement for response should be an order of magnitude
greater so a response of 7 megacycles would be a definite requirement in this
application.
This high requirement eliminates any common mechanical system consideration.
It becomes obvious that an electronic system of modulating light then is quite
necessary for a direct or real time scanning system. STAT
has considered a system of modulating continuous lasers.
This concept should be capable of modulation up to 5 megacycles. The conceived
system operates by use of building an ultrasonic transducer as a part of the
continuous laser.
In addition to the requirements for speed it is also necessary to consider the
problem of spot size. That is, it does not do any good to make 100 sweeps per
mm unless the spot has a size 1/2 of (1/100) millimeters (.0002 inches). This
size of spot would be of question and would take considerable development but
should be possible.
STAT
58
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Declassified in Part - Sanitized Copy Approved for Release 2012/09/11: CIA-RDP79B00873A001600010003-4
LIGHT SOURCES
All known UV light sources will be investigated to determine the most practical
source for projection systems utilizing a transparent luminescent screen. The
search will include, but not be limited to, the following prime UV sources:
1. Mercury Arc Lamps, High Pressure-Point Source
2. Mercury Arc Lamps, Low Pressure-Extended Source
3. Plasma
4, Laser Type in a Scanning System
5. UV Source, Optically Concentrated in a Scanning System
Compared with a Conventional Projection System.
Two extended mercury sources are to be considered. The first is a folded tube,
low pressure mercury vapor filled. Internal surfaces are phosphor coated to
0
increase the 3654A energy emittance. These UVenriched sources are approximately
75% efficient. Transmission and transmittance of the optics and filters in the
0
condensing and projection system reduce the usable 3654A energy to 10%. .Further
UV enrichment may be possible by selective construction of the extended source.
The second type is a high pressure mercury vapor in quartz or vicor tubes. This
May be enriched in the same manner, phosphor coating inside the tube. More
support equipment, ballast, power supplies, starters, etc.., are required with
0
the high pressure system. However, more 3654A energy per watt input is
available.
59
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Declassified in Part - Sanitized Copy Approved for Release 2012/09/11: CIA-RDP79B00873A001600010003-4
Lwbgi, -U4)
C T
SHEET NO. OF
E JOB NO.
IS /-1 /11 rikK5frilr
q? C ()A r
Eii-
/00T-
1 000
2, 5 0 1, 77p/4)-r
z/00 27/4
-1074-z- kADJA7te-1) Cot1E-A4
4 40 ( kt)4
3, 4-
60,
zoo ,
) ,
s- 0'7ii EtbD1E0
TO 3 )(
4