PROPOSAL FOR: MODULATED-LIGHT FILM VIEWING SYSTEM STUDY

• Document Type: CREST
• Collection: NGA Records (Formerly NIMA)
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78B04747A001100050017-7
• Release Decision: RIPPUB
• Original Classification: K
• Document Page Count: 16
• Document Creation Date: December 28, 2016
• Document Release Date: September 13, 2002
• Sequence Number: 17
• Publication Date: April 20, 1964
• Content Type: SUMMARY

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Proposal for-
Modulated-Light Film Viewing System Study
Declass Review by NIMA/DOD
April 20, 1964
STATINTL
STATINTL
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Section
I Introduction and Summary
II Technical Approach
III CRT Scanning System
IV Mechanically Scanned Light Beam System
V Enhancement Possibilities
VI Organization of the Program
VII Biographies
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1. INTRODUCTION AND SUMMARY
STATINTL This proposal is submitted I Ifor
a study of the requirements for a 11 Modulated ig h Viewing System' as
forth in the Request for Proposal believes that the selection of
STATINTL a particular system to satisfy the expressed requirements can best be made after
the completion of a study of the essential technical considerations. The proposal
submitted at this time comprises a six-month study of possible systems, including
experimental work to show the comparative performance and feasibility of certain
critical components. When the proposed study has been completed, and the various
trade-offs discussed with the contracting agency, a definite system selection will
be made and used as the basis for firm recommendations and cost estimates for
equipment development.
STATINTL
STATINTL
STATINTL
It is apparent that any system which will embody the performance capabilities which
are outlined in the RFP will require incorporation of television-type techniques.
Reasons for this conclusion are partly detailed later in this document
Section II outlines some of the main technical considerations which presently
believes of importance. It is followed in Sections III and IV by a more detailed
discussion of two definite possible approaches, to illustrate in more detail some
of the foreseen problem areas. Several of the particularly interesting technical
problems arising from the requirements for enhancement of picture areas of high
information density are outlined in Section V. The organization of the program
is given in Section VI.
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Stated briefly, the requirements for a modulated-light film viewing system
are:
a. Illumination of up to 1000 foot-lamberts with 2000 foot-lamberts desira-
ble.
b. The illumination to be modulated inversely proportional to the transmit-
tance of the film.
c. The illumination to be modulated directly proportional to the spatial fre-
quency or in other words, density of information content.
d. The size and position of the area illuminated by the modulated light shall
be independently controllable.
e. Visually perceptible flicker or smear (upon moving the film) are not
permitted.
f. Spurious effects resulting from unidirectional scan are not permitted.
It is the inclusion of requirement (c) above which rather severely constrains the
system, and yet also gives rise to some interesting possibilities discussed in
Section V., Enhancement. Without resort to conceptually involved and pro-
bably technically unfeasible schemes such as multiple parallel sensors with auto-
matic comparison of adjacent members, a sequential sampling process is required
to detect the presence of detail in a photograph. This leads to the requirement
for a scanning process, and rules out exclusive use of a semi-passive process,
such as a photo-chromic layer over the photograph. (In the present state of the
-
.art, photochromic materials are too slow-acting to meet the-requirements of no
R smear when moving the ilm~. Furthermore it is difficult to conceive how one
might increase the light behind an area of high information density without some
scanning process which would selectively illuminate the particular area with
either sufficient light to overcome the damping effect of the photochromism, or
perhaps light of some wavelength which will quench the photochromic effect. In
addition a finely resolved scanning probe would be required to detect the presence
of high information density. Hence two scanning beams are required even with a
semi-passive system. ;One advantage such a system would have over others
(particularly if an efficiently and rapidly quenchable photochromic material were
available) is that the illumination could be provided by an unmodulated and relatively
inexpensive source.
A cathode ray tube constitutes an easily modulated light source, and were it not for
requirement (c) again, a flat-face CRT in conjunction with a photomultiplier, feed-
back amplifiers, and scanning circuitry, could be made to fulfill all the system
requirements (except perhaps that of a 10 x 40 inch size). Because the spot size
need not be small, (1/2 inch has been found to be satisfactory in the Log Etronic
printer) the rather thick glass faceplate required would present no real problem.
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However when requirement (c) is introduced, a second finely focused scanning
beam must be introduced. Furthermore, the fine beam must be separated
spectrally from the illuminating beam so that it may be detected separately. This
last requirement might be avoided if the fine beam were "tagged" with a pulse
modulation and detected synchronously; however, in the presence of large il-
lumination, the signal-to-noise ratio would probably be too small to be useful.
Another system using a directly viewed flat CRT to provide illumination is pos-
sible if the fine probe is relegated to a vidicon camera imaged onto the modulated
light area. Here the presence or absence of high information density would be
detected by the vidicon which is scanned synchronously with the illuminating beam.
The automatic dodging would be provided by a photomultiplier pickup. The prin-
cipal defect with this system is that the highest spatial frequency which could be
detected would be about 1.5 cycles/mm referred to the photograph.
The spectral separation of illuminating beam and fine beam is useful also so that
the fine beam could be made invisible to the observer, and not distract him. Thus
these constraints lead to two separate cathode ray tubes imaged onto the photo-
graph and scanned synchronously. This system is described more fully in
Section III below. Its principal failing is that it is incapable of providing
sufficient illumination with presently available components, but the more de-
tailed explanation given in Section III is presented to show the main character-
istics to be considered in the proposed work for a purely electronic system.
A mechanically scanned light beam system is also conceivable and perhaps
feasible and should also be considered in the general studies. Here an intense
light source would be modulated by an optical modulator, and then made to scan
the photograph by mechanical means. This system is more fully described in
Section IV. The principal defects of this system are that the modulator is dif-
ficult and expensive to drive, no entirely suitable modulator is available, chang-
ing size and position of the modulated area is unwieldy, and without extreme mechanical
complexity, only a unidrectional scan is possible.
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III. CRT Scanning System
Main Light Source
To achieve a brightness of 1000 foot-lamberts on a 9" x 9" area from a
CRT face not in contact with the transparency requires a high efficiency optical
system. Reflection optics provide this because the effective
aperture can be made to approach the theoretical limit of f/. 5. Based on 26"
diameter the speed is about f/. 8. The light transmission efficiency, however, is
not 100 percent but something less depending on the reflectance of the mirror
and the type of lead glass (for x-ray attenuation) used in the correcting plate.
The overall light transmission of the system described herein is 20 percent. This
efficiency together with a magnification of the CRT raster (4" x 4") of 2.25 to
1 gives a 25 to 1 reduction in the light. The kinescope is rated for
25000 foot-lamberts high light brightness, which would provide 1000 foot lamberts
on the 9" x 9" area. Maximum average brightness however is only 13, 000 foot-
lamberts which .would provide maximum average illumination of the transparency
of only 500 foot-lamberts. Use of a diffuser under the film would reduce this
figure further. The CRT would be overloaded, if a transparency were viewed
which was very dense all over. To prevent this the tube would have to run at
reduced current, also reducing the light. Possibly a regulator could be devel-
oped to prevent the average ultor current from exceeding a prescribed value.
The above discussion is based on the feasibility of the design and construction of
a correcting plate for a 4' throw instead of the usual 60' to 80' throw. The
reflective optics designed for theatre TV projection when used at 4' produce ex-
cessive vignetting of the light pattern. A properly corrected plate for the 4' throw
would have to be calculated and designed.
Light from the optical system is reflected by means of a 45? mirror to the
transparency being viewed. This is done for two reasons. First, it is desirable
to adequately shield the operator from the 75 KV X-rays; second, the mirror pro-
vides a means of superposing the light from the Detail Sensor Light source. The
effect of the hole in the center of the 45? mirror is to increase the vignetting of
the main light source. The correcting plate would be designed with this in mind.
Detail Sensor Light Source
To provide a brightness modulation as a function of spatial frequency,
a detail sensor is required. A kinescope with a P15 phosphor is very well suited
for this application since the spectral characteristic of this phosphor has an in-
tense peak at 3900 A, and a broader peak at 5000 A. The longer wavelengths
could be readily filtered out to make the light invisible to the operator, and yet
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MAIN
SENSOR
MULTIPLIER
PHOTOTUBES
DETAIL 9"x 9"
CONTROLS ON FRONT SIDE
NEAR TOP
FILM
DRUM
AIR
OUTLET
LEAD
GLASS
FRONT
SURFACE
MIRROR
-USUAL FLUORESCENT LIGHTS
1/4 " LEAD
THEATRE SHIELD
PROJ. KINE. BLOWER
PROD. N P4
LENS ? REFLECTIVE
OPTICS
L.V.
AND
MU L7
V
SUPPLIE
5"
VIDEO
AND
DEFLECT.
75 KV POWER
SUPPLY
FILM
DRUM
AIR
INTAKE
Figure 1. Modulated-Light Film Viewing System
(Using CRT Light Sources)
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would be available for other uses as discussed in Section V. The persistence of
the phosphor is short, so that the relatively high frequency detection channel is
possible. (Of course the main light source would require filtering so that it
generated no light at the detail sensor wavelengths. Room lights should also be
attenuated at these wavelengths -3700 to 4100 A, to provide maximum signal-to-
noise ratio in the detail sensor channel).
75 KV Power Supply
This supply occupies about the same volume of space as the
optical system. It is shown as part of the light box in Figure 1. To reduce the
size of the light box package it may well have to be externally situated. This would
require a 75 KV connector, which is expensive.
The supply should be reliable, well protected against overload and breakdown,
should be regulated for changes of line voltage or load current, and should have
a minimum of ripple.
Deflecting Generator
The same generator would be used to deflect the beams of both CRT' s.
"Box" scanning is contemplated rather than uni-directional scanning because' it
lends itself better to enhancement effects if desired later. For example, simple
differentiation of the video signal produces a white or black edge all around an
object with "box" scanning. With uni-directional scanning the effect is lost
when the edge of the object is parallel to a scanning line. "Box" scanning is
generally used in low frame rate systems for printing pictures. For direct
viewing with no flicker deflecting circuitry would have to be developed. This is
not considered difficult.
The problem here is to place the sensors in such a position that they
will sense the area of the transparency under the viewing microscope, yet not
obstruct the view. To mount the sensor directly on the microscope would simplify
the problem but complicate the microscope. To take care of both direct and
microscope viewing the best compromise seems to be to mount them on the side
of the 9" x 9" area at a low viewing angle (see Figure 1). This means that
corrections such as graded density filters will have to be made to minimize
shading.
Multiplier and Low Voltage Power Supplier
These suppliers are conventional and may be purchased from any suitable
vendor. They could be mounted on the sides or ends of the viewer or in a remote
package along with the 75 KV supply if desired.
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Video and Processing Amplifiers
The video amplifier for the Detail Sensor would be wide band but no
difficulty is anticipated. The corresponding amplifier for the main sensor would
be narrow band and would be conventional. Video processing may not be re-
quired with "box" scanning. If it is, circuitry would have to be developed for
this type scanning.
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IV. Mechanically Scanned Light Beam System
The use of a modulated light beam with mechanical scanning represents a
possibility, and is described below.
Such a method of scanning with a modulated light beam is shown in Figure 2. This
technique, as shown, scans the 9" x 9" area unidirectionally. Being unidirectional,
the position of the probing light can be adjusted with respect to the position of the
illuminating light. Thus, if the modulation response delay is prohibitively large,
the probing light can be advanced to compensate for this delay.
Due to the required tolerances this would require extremely fine adjustments. The
synchronization of the multifaced reflectors would also require extremely fine ad-
justments. The rotational speed of the high speed mirror drum is inversely pro-
portional to the size of the illuminating spot size and the number of faces on the
mirror drum, but in the range of spot size considered, the speed of the high speed
mirror drum will not be prohibitively large.
The optical system, as shown, is compact and should readily fit inside the standard
size viewers with little problem.
Unmodulated areas on both sides of the modulated area could have separate controls.
It may be desirable to have clear glass instead of opal glass for the modulated area
depending upon the beam requirements.
Though it is not shown in the figure, various methods for reducing the size of the
modulated area have been investigated. One of the methods would be to have
several multi-faced reflectors on each shaft. On any one shaft, each reflector
would have a different number of faces. Rotating at the same speed, the total
amount of illumination would be scanned over a smaller area. This shifting of
reflectors could by accomplished readily without varying the speed of rotation.
Another method would involve the insertion of different condensing lens systems.
It is conceivable that the entire optical system could be balanced in such a manner
that would allow translation of this smaller modulated light area to any position
in the original larger modulated area.
The scanning frequencies in the system as shown can be adjusted for interlacing
and overlap if required.
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DETAI L
MAIN SENSOR
SENSOR MULTIPLIER
PHOTOTUBES
N, 9"x9"MODULATED
AREA
LOW SPEED
MIRROR
DRUMS
ILLUMINATING
LIGHT SOURCE
HIGH SPEED LIGHT
MIRROR DRUM MODULATOR
Figure 2. Mechanical Scanning Technique Using
Light Modulator
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STAT
STAT
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Methods for bidirectional scanning has been investigated in order to overcome
the problems of uni-directional scanning. One possible method of obtaining bi-
directional scanning is with the use of counter-rotating multi-faced reflectors.
There would be problems with synchronization inherent with such a system.
The problem of modulation of the light beam is a difficult one. When a scanning
speed is used which is fast enough so that there is no flicker, the modulation
bandwidth capability should be approximately 360, 000 c. p. s. This high modula-
tion rate rules out mechanical modulation methods. An electro optical light
modulator of crystal can be made to
function effective y at these frequencies, but is not entirely suitable for several
reasons.
The modulation is accomplished by varying the retardation of a polarized light
beam, and thus requires two polarizers which are only about 35% transparent
at best. The cell itself is about 80% transparent, and hence for the large light
flux required absorbs sufficient heat that special cooling would be required (max
operating temperature is 900F).
The modulation is accomplished by varying the voltage applied across the cell.
For 5:1 modulation about 3500V peak-to-peak swing is required. Certainly this
is not easily or cheaply accomplished.
A further disadvantage of this type of modulator is that when white light is used,
the spectral content will change as the potential across the cell is varied. This
fact results from the characteristic that the retardation is greater for shorter
wavelengths.
Other types of light valves are possible. Perhaps the most promising of these
is the ultra-sonic light valve, but it too is not entirely suitable.
Much research is being conducted currently in this field, particularily in con-
nection with the problem of modulating laser beams, and breakthroughs may be
imminent.
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V. Enhancement Possibilities
There are several peripheral effects which are available as a consequence
of the use of a five probe scanning beam for detection of high information density.
Because the diffuse illuminating beam and the fine probe beam are scanned syn-
chronously, there will be considerable space between adjacent traces of the fine
beam. If a small region of high information density were to fall between these
tracks it would not have its illumination increased as desired. However it is
possible that the fine beam track could be moved back and forth within the diffuse
beam track at a cycling rate of a few cycles per second. The effect of this op-
eration, which would be at the discretion of the operator, would be that such
small regions would scintillate in brightness at the cycling rate, and the observer's
attention would be drawn to them.
Another effect which might have value under certain circumstances is that the
fine probe light could be made visible (by removal of filters), and not used for
its normal purpose, but instead be made to superimpose on the main illumination
a regular dot on line pattern which would beat with regularities in the photograph
to form a moire pattern, and hence aid in detecting such regularities. The
relative ease with which the spacing of the superimposed pattern might be changed
would perhaps aid in finding a suitable one for the particular regularity to be
detected.
It might also be possible that the fine beam could be used in limited areas to
perform an effective contrast expansion of fine detail within its limits of reso-
lution. It is envisioned that this effect would be used for close inspection, and
could be implemented with modified use of the installed feedback amplifiers.
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STATINTL
STATINTL
STATINTL
STATINTL
STATINTL
VI. ORGANIZATION OF THE PROGRAM
A six month study program involving the efforts of approximately two
members of the technical staff, plus a ro iate support, is proposed. The
work will be the responsibility of the
members of the group have full use of both the
specialized facilities
0
STATINTL General program management will be the responsibility of Manager,
Physical Research. The project engineer Biographies of
STATINTL the above and others who are expected to be associated with the project are
appended.
The work will consist of theoretical and limited experimental studies resulting
in firm recommendations for prototype equipment development. By limited
experimental studies is meant performance of such experiments as are deemed
necessary to prove any calculated results where parameters are insufficiently
well known to yield theoretical answers of high confidence, or where subjective
evaluation is required in order to determine whether a particular technique is
suitable.
It is felt that a completely operating breadboard may not be necessary for
system design provided that all parts and functions of the system have been
demonstrated and/or calculated with good confidence. The proposed program
of work is as follows.
A search and study will be ll ade of all applicable
phenomena, followed by more intensive study of the
more promising techniques9 some of which are expected
to include those listed below.
A study of the characteristics of photochronism and other
semi-passive phenomena will be made to determine whether
very recent improvements makes their use more attractive.
Methods of improving the spatial frequency sensing resolution
of a CRT-vidicon camera system will be investigated. If the
resolution were improved, this system might be the most
suitable.
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A study of the projection CRTs stem will be performed.
Modified use of available optics will be studied,
taking into account the partial reduction of vignetting
resulting from the use of negative feedback in the system.
A study will be made of the subjective effect of the presence
or absence of a diffusing layer directly under the film.
A study will be made of the subjective effect of smear and
flicker at various light levels, spot persistences and
scanning patterns and rates.
A study will be made of the mechanically scanned light
beam system. In particular the optical system parameters
will be investigated to determine closely source intensity
and modulator flux requirements. Various modulator types
will be re-examined to determine optimum type, and if
necessary formulate specifications for a specific design.
Studies of methods and cost of implementing the enhance-
ment effects proposed will be performed if the customer
deems that they are of sufficient value.
A study of application to modulated-light rear-projection
screen viewing will be made, and recommendations set
forth. A proposal for development of this type of equipment
will not necessarily be presented.
Monthly letter reports describing progress will be submitted.
A final report will be submitted including a firm recommendation
for a specific system, including a budgetary estimate for
building a working breadboard or prototype. If the customer
should desire a firm estimate for this work=ill be pleased
to furnish same at no additional cost.
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 STATINTL
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