DEVELOPMENT OF AN IMPROVED HIGH INTENSITY HIGH RESOLUTION SCREEN FOR REAR PROJECTION
Document Type:
Collection:
Document Number (FOIA) /ESDN (CREST):
CIA-RDP79B00873A001600010002-5
Release Decision:
RIPPUB
Original Classification:
K
Document Page Count:
53
Document Creation Date:
December 28, 2016
Document Release Date:
September 11, 2012
Sequence Number:
2
Case Number:
Publication Date:
September 20, 1963
Content Type:
MISC
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DEVELOPMENT OF AN IMPROVED
HIGH INTENSITY HIGH RESOLUTION SCREEN FOR
REAR PROJECTION
?
STAT
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STAT
DEVELOPMENT OF AN IMPROVED
HIGH INTENSITY HIGH RESOLUTION SCREEN FOR
REAR PROJECTION
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STAT
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SIN31NO3 JO 3181,1
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TABLE OF CONTENTS
LETTER OF TRANSMITTAL
COST QUOTATION
TERMS AND CONDITIONS
1 INTRODUCTION
2 OBJECT OF SCREEN RESEARCH AND DEVELOPMENT WORK
3 FEASIBILITY DEMONSTRATION
4 DETAILED WORK STATEMENT
5 PROJECTION 'SYSTEM FOR FINAL FEASIBILITY DEMONSTRATIONS
6 SUGGESTED FURTHER STUDIES BASED ON OUTCOME OF ABOVE WORK
7 PROGRAM SCHEDULE
APPENDIX
TECHNICAL DATA
Miscellaneous Properties
Percent
Transmission vs
Wavelength
for
Cronar Film
.007"
Percent
Transmission vs
Wavelength
for
Cronar Film
.005"
Percent
Transmission vs
Wavelength
for
Cronar Film
.004"
Density vs Wavelength for Type 5430 Film
Density vs Wavelength for Type 5427 Film
CAPABILITIES
Available Equipment at
RESUMES
:esearch Center
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L. STAT
Main Post Office Box 2143
Washington, D.C.
Subject:
Reference:
Gentlemen:
High Resolution Projection System
Letter Proposal 3-1303
Proposal 3-1303A
Thank you for your verbal request for a further proposal on a high resolution
projection system. The present proposal is basically a research and development
program centered on the development of a suitable fluorescent screen for such
a system. The basic idea of this proposal has been tested by
and a patent has been applied for. The development of the
the point where it is readily reproducible. In the
course of the program-a suitable projector and optical system will be designed
to excite the screen.
screen will be taken to
A complete cost breakdown for the work specified is attached, together with a
time schedule. The costing of the program is based on a cost-plus-fixed-fee
contract under the Armed Services Procurement Regulations, appropriate details
are enclosed.
The basic research
work
work will be a
with The
our facilities
on the screen materials will be done at the
as they are ideally equipped to do this work. This
subcontract: however, the overall program control and direction
and located close to
easily maintained.
enabling control and liaison to be
ill submit monthly progress reports, in addition to a final report, on
the findings of the whole program.
Just prior to the submission of this proposal we received your samples of
Type 5247 and 5430 film. We have run density versus wavelength tests on these
and the graphs are included in the Appendix under Technical Data.
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remains
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Washington, D. C.
At your request, has limited
posal to the home office in
the
distribution of
20 SeptembISTAT53
Page 2
information regarding this p:STAT
STAT
Should you have any questions regarding this proposal, or require either additional
information or a local contact, please do not hesitate to contact us.
WDS:ek
Sincerely,
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3-1303B
TERMS AND CONDITIONS
(Cost-Plus-Fixed-Fee Researchand Development Contract)
Terms and Conditions substantially in agreement with the Armed Services Procure-
ment Regulations would be acceptable to under STAT
any Cost-Plus-Fixed-Fee Research and Development Contract resulting from this
proposal.
It is requested that the following provisions be incorporated in the resulting
contract.;
1. "Stop Work Orders!' Clause ASPR 7-404,5
2. Contractors Independent Research Programs
a. Any invention made in the performance of any work by the
Contractor under the Contractor's own product improvement
program or the Contractors Independent Research Program,
even though supported by an allowance of costs for such pro-
gram as a part of the overhead costs hereof, will not be sub-
ject to the "Property Rights in Inventions" clause of this
contract unless said work is identified in writing as being
required in the performance of this contract.
b. The concept contained herein is
regarded properietary and
retains all rights to
concept.
commercial applications of the
3. Payment - Net within 30 days after date of invoice.
4. Payment of the fixed-fee under this contract shall be made in monthly
installments. Each installment shall bear the same proportion to the
total amount of the fixed-fee asthe_proportion of work completed at
the date of such claim bears to the total work called for under this
contract.
5. Reimbursement and settlement of overhead expenses shall be on an
actual rate as established by the cognizant Government audit agency.
Pending establishment of the final overhead rates for any period,
provisional reimbursement will be made on the basis of billing rates
approved by the cognizant Government Auditor.
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TERMS AND CONDITIONS (Continued)
[: (Cost-Plus-Fixed-Fee Research and Development Contract)
STAT
STAT
3-1303B
6, "Authorization and Consent" clause ASPR 9-102.2.
7. "Patent Rights" Clauses ASPR 9-107.1(a), 9-107.2(a) and 9-107.2(b).
8. Authority to Subcontract - Sole Source Subcontract Approval,
is hereby granted approval to subcontract to
STAT
STAT
as a sole source subcontractor, a portion of STAT
the work on a Cost-Plus-Fixed-Fee basis.
General - cognizant Government Audit Agency is the Air Force Auditor
General in coordination with Administrative Contracting
Officer, Headquarters, Los Angeles Contract Management District.
STAT
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C
1. INTRODUCTION
Our earlier proposal Register No. 3-1303A, was for a system designed to STAT
increase the rate of information transfer from a projected film image to an
observer. The proposal covered areas of research which would improve screen
resolution by using new screen materials, new projection techniques and by
investigating certain physiological responses.
This proposal Register No. 3-1303B is specifically for a research and STAT
development program to produce a high intensity, high resolution fluorescent
screen of optimum performance for the rear projection of a black and white
film image. The light source used for projection will be strong in ultra-
violet as well as visible light.
requests that the concept contained herein, and the successful developmeniSTAT
of an improved screen be regarded as proprietary and retains all rights to
commercial applications.
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2. OBJECT OF SCREEN. RESEARCH AND DEVELOPMENT WORK
The object of this research and development work, as detailed below, is to
produce a high resolution, rear-projection screen of improved performance.
The proposed screen will comprise a layer of fluorescent material on a glass-
like substrate and will have a high degree of transparency to visible light.
Tests will be performed to determine the optimum illumination of the screen
to provide the maximum rate of transfer of information.
It will be illuminated by:
a Ultraviolet light alone so that a visible linage may be formed on
the screen.
b. Visible light alone so that an aerial image can be formed and
transmitted through the screen and viewed by a supplementary magnifier
in front of the screen.
c. A combination of visible and ultraviolet light, the aerial and visible
linage as formed being brought to a focus in the same plane.
A projector lens corrected for the ultraviolet and the visible is necessary
for the above experiments.
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3. FEASIBILITY DEMONSTRATION
To demonstrate the feasibility of the screen small samples a few inches square
will be used. From these an initial evaluation will be made to determine image
quality using ultraviolet light,viewing.
Final evaluation of the best samples will be made using a projector having high-
power ultraviolet and visible light sources and which will achieve the magnifi-
cations required in practice.
The above is discussed in detail in the following work statement.
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41.=
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4. DETAILED WORK STATEMENT
Make necessary jigs and fixtures.
b. On a suitable, transparent glass-like substrate make trial coatings
of zinc sulfide and cadmium tungstate by vacuum deposition. Coatings
will be of zinc sulfide activated with copper, chlorine, phosphorus
or arsenic, and of cadmium tungstate with tungsten or manganese
activator.
.In parallel with the above an extensive search of literature will
be made to determine what (applicable to the project) has been done
in this field and whether there are more promising materials which
should be tried.
d. It is also proposed to make organic luminescent coatings of anthra-
cene, fluorene, rubrene, diphenylcyclo-octatetraene and umbelliferone
in an acrylic resin or a polycarbonate resin.
e. These samples will be tested using ultraviolet stimulation and
measurements made of visible emission brightness.
f. An evaluation of the best of these coatings will be made to determine
image quality using a small ultraviolet projector which is currently
available and whether sufficient resolution and brightness can be
obtained for direct image viewing.
?A feasibility demonstration will be carried out using a projector with
a lens corrected for ultraviolet and visible light. The film frame
will be projected on an area of at least 30 by 30 inches and an evalu-
ation will be made of the visible image, the aerial image and the
composite image formed by the ultraviolet and the visible light.
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4.1 CHARACTERISTICS OF THE FILTERING
a. For transmission of ultraviolet (UV) in the rpion required to excite
a phosphor sensitive in the region 3500-4000 A. This would be a com-
bination absorption filter having a characteristic as shown in Figure
1. The broken line is transmission by the lens materials and the full
line is transmission of Corning 7-54 filter. The shaded area repre-
sents transmitted UV.
% RELATIVE
TRANSM I SSI ON
350 400
WAVELENGTH (Mg)
FIGURE 1
Percent Transmission for Corning
7-54 Filter and Lens Material
450
500
This combination would be used if it proves feasible to view the over-
all scene and to study in detail an area of interest using luminescence
of the screen only as discussed
b. For transmission of both UV for exciting the phosphor, and visible for
specular viewing, the filtering curve in Figure 2 would apply. Here
the broken line is the lens and full line is a filter-like Balzer
1256/283 CALFLEX Bl/Kl.
4.2 CONTRAST TRANSFER FUNCTION GOAL
Preparation of three types of luminescent screen is planned. These will be in-
organic transparent, inorganic diffuse and organic transparent. Brightness of
ultraviolet stimulated visible emission will be measured by a photocell. Resolu-
tion capability will be evaluated by standard resolution test pattern image
observations.
t= 4-2
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% TRANSMISSION
100
80
60
40
20
STAT
300 400 500 600 700 800
WAVELENGTH (Mg)
FIGURE 2
Percent Transmission for mv and Visible for Lens and
Filter Balzer 1256/283 CALFLEX Bl/K1
To measure contrast transfer function would require use of a specialized micro-
densitometer, which we do not have. As the result of this program we shall be
able to define the requirements for the apparatus to make these measurements.
This may form the basis for a separate proposal in which we would undertake to
compare performance of the screens produced in this work with those in the prior
art.
4.3 FILM BASE AND EMULSION OPTICAL CONSIDERATIONS
Information has been obtained concerning Eastman 5427 Aerographic duplicating
film which has a cellulose acetate butyrate base and also for Eastman type 8427
Aerial Recon. duplicating film which has a cellulose tri-acetate base.
Curves are shown in Figure 3 below, for spectral transmission of base alone and
of processed unexposed base with emulsion. The curves show that transmission
does not vary greatly throughout the spectrum of interest. Curves for other
materials are included in the Appendix.
H&D curves of density versus exposure for various processing procedures (see
Figure 4 below) show that, for faithful reproduction of the original film, the
range of transmission of the film may be from 607 (D = .22) to approximately
.17 (D = 3.0) or about 600:1.
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% TRANSMISSION
100
80
60
40
20
CELLULOSE
ACETATE
BUTYRATE
STAT
5247
200
250 300 350
WAVELENGTH ( MI0
FIGURE 3
Percent Transmission versus Wavelength
4.4 PHOSPHOR CONSIDERATIONS
4.4.1 INORGANIC PHOSPHORS
400
A literature search for figures relating luminescent yield of phosphors for
incident energy so far has yieldedolittle 4:formation on transparent phosphors
excited by near ultraviolet (3500 A - 4000 A). Extensive discussions are given
for diffuse or crystalline surfaces which are commonly used for TV and instru-
mentation cathode ray tube phosphors. These phosphors are generally excited by
electron beams and information relating to ultraviolet excited emission has been
mostly qualitative. In general, manufacturers of phosphors regard ultraviolet
stimulated visible emission as weak, compared to electron beam excited emission,
yet it may be adequate for our purpose.
One reason for the weak emission of transparent phosphors is that a single
passage of the ultraviolet does not allow much path length for absorption. For
diffusion crystalline phosphors a much greater path length is traversed due to
multiple internal reflections in the crystals. For transparent phosphor screens,
emission of light measured in the direction of the viewer is about 25 to 507 of
the total emitted by the phosphor.
4.4.2 ORGANIC PHOSPHORS
Organic luminescent materials have been investigated much more fully because
absorption of ultraviolet and emission of visible and ultraviolet are used as
a tool for analysis of organics. However some materials which luminesce in
liquid solution will not do so in solid solution. For others the converse is
true. Also increase of concentration in solution sometimes results in a decrease
in emission.
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ILLUMINANT: TUNGSTEN
DEVELOPMENT: DK.50 AT 68? F ?
(20? C) IN
SENSITOMETRIC
MACHINE
0.0
1.0
LOG EXPOSURE
FIGURE 4
Percent Transmission versus Density
2.0
3.6
3.2
2.8
2.4
2.0
1.6
1.2
.8
DENSITY
STAT
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5. PROJECTION SYSTEM FOR FINAL FEASIBILITY DEMONSTRATION
In conjunction with the above work a projection system will be designed capable
of handling up to a 2.5 KW light source and yielding ultraviolet as well as
visible light, with suitable filters therefore, it will be possible to excite
the fluorescent screen with ultraviolet or visible light or both.
To prevent damage to the film due to heat, infrared transmitting mirrors and
infrared filters will be incorporated in addition to refrigerated air cooling
as may prove necessary.
The projector will illuminate a screen area of at least 30 by 30 inches so
that any fluoresent sample under test will receive the energy per unit area
that would be experienced in practice.
In order to test the full capabilities of the screen, a projector lens will
be designed so that the ultraviolet and visible light are brought to a sharp
focus on the screen. The lens will therefore be corrected over the range from
35001 to 60000X and will also have a resolution of 200 lines per mm. The
maximum magnification of the projector system will be approximately 50 times.
An additional optical system may be used in front of the screen so that quality
of the visible linage formed by the ultraviolet and the aerial image formed
by the visible can be evaluated both independently and together. A minimum
of four spectral interference filters will be provided to select appropriate
wavelengths for the viewing of the visible light.
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6. SUGGESTED FURTHER STUDIES BASED ON OUTCOME OF THE ABOVE WORK
Should successful single layer fluorescent screen samples be developed, follow-
up work and studies should encompass:
a. The technique of making larger screens of approximately 30 by 30
inches should be mastered
b. Screen samples having multiple coatings should be developed and
evaluated. Such screens could render density levels in the form
of color.
c. The basic objective of obtaining maximum information transfer from a
projected film image to an observer should be followed up using the
maximum number of observer sensitivities.
For example, the intensity of light on a multiple coated screen
could control the depth to which light penetrates. Using coatings
flourescing at different wavelengths, and using color-separating
filters, an observers perspective detecting faculty could discern
density levels.
Other physiological responses, which were discussed in the previous
proposal 3-1303A, and which could be applied to the viewing of a
fluorescent screen, should be investigated in order to produce an
optimum overall system.
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7. PROGRAM SCHEDULE
The PERT diagram (Figure 7-1) depicts a summarized program outline. See
Figure 7-2 for Program Organization.
At the end of the first 3 weeks of the program a sufficient evaluation of the
initial coatings will have been made so that the design and procurement of
projector parts can proceed.
Continued studies and work on experimental screen coatings will take place in
parallel with the projector lens design, and projector procurement and assembly.
This phase of the work will cover a period of thirteen weeks.
The time spent on the literature survey of screen materials etc., will be
about 120 hours. This time will be spread over a period of 16 weeks as shown
on the PERT diagram.
Final evaluation of the best screen using the projector with a 2.5 KW light
source, and necessary filters etc. will take place over a 6 weeks period.
s uniquely suited to accomplish the tasks required in this proposal. STAT
A description of the background and facilities can be found in the Appendix.
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LITERATURE SURVEY OF SCREEN MATERIALS
DESIGN
OF JIGS
AND
IXTURE
PROJECT AND PRO-
ORGANI2- ? CUREMENT
ATION OF
PHOS HORS
I WEEK
I.WEEK
EVALUATION
? OF INITIAL
COATINGS
CONTINUED WORK ON
EXPERIMENTAL COATING AND
MEASUREMENTS AS SAME
FINAL EVALUATION
AND FEASABILITY
STUDIES OF BEST SCREENS
2 WEEKS
PROJECTOR LENS DESIGN AND
LENS MANUFACTURE
AND ASSEMBLY OF
PROCUREMENT OF
PROJECTOR PARTS
8 WEEKS
PROJECTOR SYSTEM
WEEKS
FIGURE 7-1
Program Outline
6 WEEKS
0 FINAL REPORT 0
2 WEEKS
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25 WEEKS
STAT
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11/1HIWAL jr rrIYc.ML,urt
KODAK AERIAL AND SPECIAL SENSITIZED MATERIALS 11 1
MScrD.iflirs Pr.pertes
Section 11 0 Optical Properties
This section presents data on the optical characteristics of aerial
films which might be of some use in the design of special photographic
systems, or of value in the interpretation of effects. The spectral trans-
mittance of film base and emulsion-coated films is given, together
with typical values for haze, as it might affect the clarity of negatives,
printing techniques, etc. The indexes of refraction of cellulose ester
and Estar polyester bases are of practical importance in their effect on
the fogging of aerial films by accidental edge illumination, and on
image resolution.
A. SPECTRAL TRANSMITTANCE
The spectral-transmittance curves for cellulose ester and Estar bases,
and for various aerial films which have been developed and fixed
without exposure, are given in Figures 11-1, ?2, ?3, and ?4.
Both types of base show a sharp cutoff in the ultraviolet region
(Figure 11-1). The cellulose ester base does not transmit below about
270 millimicrons, or the Estar base below 315 millimicrons. In the
visible region both types of clear base show excellent clarity with
high, uniform transmission. In the case of the gray triacetate base
the spectral transmission is affected by the dyes incorporated for
antihalation purposes (Figure 11-3).
Estar and cellulose ester bases show high transmission in the
near infrared region out to 2 microns wavelength (Figure 11-4).
Between 2 and 15 microns there is considerable variation in trans-
mission with wavelength. In this region the infrared .absorption char-
acteristics of the particular polymer are of value in analytical deter-
minations of structure and composition, but are probably not of
practical importance in photographic applications.
The transmittance values for emulsion-coated films developed
and fixed without exposure show changes from the base curves in
june 1961
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the ultraviolet and visible regions (Figures 11-2 and 11-3). The
transmission is slightly reduced as a result of residual traces of back-
ing dyes and emulsion silver. Transmission in the near infrared
region is not significantly affected by the presence of the fixed-out,
clear gelatin layers (Figure 11-4).
The data in Figures 11-1, ?2, ?3, and ?4 are based on total
transmission. Measurements comparing the total, or diffuse-light,
transmittance with the specular-light transmittance show the latter to
be only 2 to 3 percent less for the film bases and for films that con-
tain no matte in the emulsion or gel backing. Where a matte is
present in the fixed-out film, the specular transmittance averages
12 to 15 percent less than the total transmittance.
B. HAZE
Extremely fine particles dispersed in the film base or gel layers act
just as atmospheric haze does in the scattering of light rays. "Haze"
is defined as that percentage of transmitted light which, in passing
through a sample, deviates from the incident beam by fOrward scat-
tering, i.e.:
Scattered Light
% Haze =
Total Transmitted Light x 100
It may be measured by a hazemeter or recording spectropho-
tometer, as described in American Society for Testing Materials,
Method D 1003-59T.
Typical haze measurements for film bases and unexposed proc-
essed films are shown in Table 11-1. Both cellulose ester and Estar
bases are quite free from light-scattering effects, and the haze of
clear, processed films that contain no matte is generally less than
I percent. In the gel-backed films a matte is incorporated to reduce
intimacy of contact between laps of film and to avoid Newton's rings
in printing operations. This matte results in haze values of 8 to 12
percent. The practical effect of this amount of light scattering is not
ordinarily significant in the use of the films. Matte particles are not
resolved except under conditions of very high magnification (80 to
100X). However, it must be recognized that haze might cause some
slight loss of resolution in printing operations under very critical
conditions involving specular illumination.
C. REFRACTIVE INDEX
The refractive indexes of film components are probably of practical
interest only in very special cases where the design of systems re-
quires recognition of this optical property. Typical values for refrac-
tive index are as follows:
r ,
Cellulose Ester Bases
Estar Polyester Base
Vertical axis
Perpendicular to major axis in.olane of sheet
Major axis in plane of sheet
Gelatin
N.,
Nr
Refractive Index
ND
1.48
1.50
1.64
1.66
1.50- 1.54
A material which exhibits variations in refractive index in dif-
ferent directions is said to show birefringence. Because of the biaxial
stretching of Estar base in manufacture, it exhibits this behavior.
As shown above, the greatest difference in index of refraction is be-
tween the thickness direction and the plane of the sheet. Differences
in the plane of the sheet, not necessarily in the length and width
directions, are slight and generally less than 0.02. The effect of this
slight difference in orientation on dimensional stability of Estar base
is discussed in Section 9. The birefringence of cellulose ester bases
is almost negligible, being of the order of 10-5.
D. EDGE FOG
A very practical effect of the difference in refractive index between
cellulose ester and Estar bases is in the extent of film fogging which
may result from exposure of the film edges to light and consequent
"piping" of the light through the film base. This is entirely separate
from film fogging by accidental exposure of the emulsion surface
to light.
When the ratio of refractive index of the gelatin coating to the
base is less than 1.0, as in the case of Estar base film (m=1.54/1.64),
efficiency of internal reflection within the base is high over a wide
range of incident angles. Where the ratio is greater than 1.0, as with
cellulose ester base films (m=1.54/1.48), efficiency of internal re-
flection is much lower. Therefore, much of the incident light striking
the edge of Estar base is propagated through the base and is attenu-
ated only gradually by absorption within the base and by refraction
at the gel interfaces.
Any light refracted out into the emulsion fogs the film. This
may take the form of a fog density uniformly decreasing with dis-
tance from the edges or, under certain geometric and optical con-
ditions, the light may be lost from the support to the gel layers in a
repeating wave form, resulting in a striated fog pattern.
The high efficiency of light propagation through Estar base,
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(11classif1ed in Part -Sanitized Copy Approved for Release 2012/09/11 : CIA-RDP79B00873A001600010002-5 Pei mir 1,3%
compared with cellulose ester base, is the same as in polymethyl
methacrylate and certain other plastics. Here, the phenomenon is
utilized in medical applications, such as the bronchoscope, or as
rod extensions on flashlights. This effect is evident on viewing a roll
of Estar base Alm from the side, where light transmitted through the
edges of the film base is visible.
These effects are illustrated in exaggerated form in Figure 11-5
which shows the fog produced in various films that have all been
given the same edge exposure in a laboratory comparison test. These
films, shielded on the emulsion and base sides, were given a con-
trolled exposure, with the illumination directed at the cut edge of
the filrns. While there is a fixed, inherent characteristic of Estar
base to "pipe" light, the actual depth of fog penetration is influ-
enced by the emulsion speed. As the "piped" light attenuates with
distance the threshold exposure of slower emulsions is reached sooner.
This is indicated by the lesser penetration of fog in the slower Experi-
mental High Definition (S0-132) and Experimental Panatomic-X
(S0-130) Aerial Films, compared with the Experimental Plus-X
(S0-102) Aerial Film, though all are on the same Estar base.
Penetration is likewise affected by any absorbing or diffusing
addenda in the base, such as haze, dye, or pigment. The gray cellu-
lose triacetatc base very effectively stops the light penetration, as
illustrated with Special High Definition Aerial Film (S0-243) in
Figure 11-5.
The above laboratory test is deliberately exaggerated. Figure
11-6 illustrates the effect of the base type on edge fog penetration
under more practical conditions. Rolls of film with a clearance of
0.025 inch between the edges of the roll and the spool flange were
exposed to an illumination of 2240 foot-candles for 4 minutes. A
certain amount of the light was reflected from the inside of the flange
at the proper incident angles to penetrate the film base and fog the
emulsion, as illustrated. The Estar base film shows slightly deeper
penetration than the triacetate base films.
The increased fogging potentiality of polyester base films points
out the need for prevention of accidental edge exposure. However,
in normal practice aerial films are wound on flanged spools and
loaded in cameras or magazines in the dark or in subdued light.
Under these conditions edge fog, even with polyester base film, is
not a problem.
E. IMAGE DEFINITION
The higher refractive index of Estar base compared with cellulose
ester bases, may result in very slightly lower definition under some
special circumstances. This is primarily because the ratio of the
refractive indexes of the gel layer?Estar base combination is greater
than this ratio for the gel layer?cellulose ester base combination.
This effect is not significant in the case of camera negatives, as
the image is normally formed by exposure of the emulsion surface.
Resolution would only be affected by light penetrating the unproc-
essed emulsion, with reflection from the back of the base or the back
of an anti-halation gel layer. Thus, in camera negative films, the
type of base has no significant effect on image quality.
In the case of contact printing, in which the illumination comes
through the base, optical characteristics of the base may have a
small effect. Microscopic examination of resolution-chart images
printed through both Estar and cellulose ester bases shows no differ-
ence in sharpness, for film of normal resolution. As would be ex-
pected, images printed with specular light are sharper than those
printed with diffuse illumination, for both types of base. In the
unusual case of successive generations of duplicating by contact
printing, using film of very high resolving power (e.g., SO-l05),
some small loss in definition occurs.
The following table illustrates that with a very high resolution
film, a greater loss occurs in contact printing by specular than by
diffuse illumination. It also shows the difference in loss for the two
types of bases.
First Negative
First Print
Second Negative
Specular
Diffuse
Specular Diffuse
Cellulose Ester Base
390 lines/mm
360
360
330 330
Estar Polyester Base
390 lines/mm
330
360
270 330
Both before and after exposure and processing, the emulsion
has some turbidity; consequently, some light is always traveling
towards both surfaces at varying angles. It is this light that is
multiply-reflected to produce the image degradation.
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