IMPROVED SCREEN FOR REAR PROJECTION VIEWERS

• Document Type: CREST
• Collection: NGA Records (Formerly NIMA)
• Document Number (FOIA) /ESDN (CREST): CIA-RDP79B00873A002000010010-1
• Release Decision: RIPPUB
• Original Classification: C
• Document Page Count: 15
• Document Creation Date: December 28, 2016
• Document Release Date: November 8, 2012
• Sequence Number: 10
• Publication Date: October 15, 1965
• Content Type: REPORT

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reproduced or (2) distribu7outside
without permibsion of the 25X1
CONFIDENTIAL
divisional security representativ4"
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DOES PAT
CORNING GLASS WORKS
ELECTRO?OPTICS LABORATORY
RALEIGH, NORTH CAROLINA
IMPROVED SCREEN FOR REAR PROJECTION VIEWERS
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/Technical Report No.:
Date:
Period Covered:
3
10-15-65
9-15-65
to
10-15-65
THIS OCr2.N.r.c.41 Af7r.;11111
THE S [AiflIlIN
THE ?:.:1 'Int.':i, LSC.,
SECTIONS 7E3 AND 794 TVir.
TION Of 11/HCH IN ANT IV,1,NNES1 10 AN inIAUVHOctIZED
fliiSON PROHISITSD EY LAW.
?CONFIDENTIAL
25X1
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Table of Contents
I. Accomplishments
1. Literature Search
A. Open Literature
B. Patent Literature
2. Preliminary Theoretical Investigation
A. Screen Resolution
3. Familiarization with Corning Manufacturing
Facilities
A. Glass Ceramics
B. Photosensitive Glasses
C. Multiform Glasses
D. Porous Glasses
E. Optical Fibers and Matrices
4. Progress on Rear View Screen Materials
A. Manufacture of Hollow Fibers and Matrices
(7) B. Metallizing of Hollow Fiber Cores
C. Losses in an Uncoated Hollow Glass Fiber
II. Next Period Objectives
1. Literature Search
2. Familiarization with Corning Facilities
3. Outline of Future Program Planning
4. Instrumentation
fr'g
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\N_y:
I. Accomplishments
1. Literature Search
A. Open Literature
The reading and assimilation of this is near
to being concluded. The articles directly
related to rear projection screens and their
performance is being condensed into a single
complete treatment. From this foundation
various areas will be defined requiring
either new or further theoretical work
which will be undertaken in the next phase
of the program.
The other articles which have been obtained
relate to the measurement of the scattering
function and theoretical developments relating
to scattering theory and the effects of
particle size, refractive index, and
concentration on the scattering function.
Also there are many good articles on tech-
niques which allow the determination of the
physical parameters of the particle given the
desired scattering function.
B. Patent Literature
The patent literature has been read and digested.
It contains 43 different articles; of these,
only 27 relate specifically to screens. The
other 16 articles cover such topics as
baffeling to protect against strong ambient
light, portable structures to support various
screens, and a variety of other unrelated topics.
Those patents directly relating to rear projection
screens can be classified as follows:
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1) Lenticular Screens
a. General
b. Designed to rlaalice_the_tQhal_internal
U....f.12S112n-2f-llatI_I.U2R2J-1.1t1Eagn
the two surfaces.
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to ambient light.
2) Fresnel Screens
a. Screens made up of Fresnel surfaces.
b. Fresnel surfaces used in conjunction
with other lenticular elements and
diffusing layers.
3) A new type of rear projection screen which
combines the advantages of both front and
rear screen but does not have their
disadvantages.
Techniques to accomplish dynamic scanning
of projection screens.
5) Techniques used in making screens.
These topics will be discussed in detail in the
interim report which will be part of technical
report #4.
2. Preliminary Theoretical Investigation:
A. Screen Resolution
After presenting the mathematical foundations
of modulation transfer function theory and
considering conventional techniques compatable
for measuring the MTF of rear projection screens,
there see _? ffio ustific tion f thinki g
tra_fatantialiaDaiDlagUEZ-1E-MaRiL.O.
Certain conventional techniques are not
applicable to projection screens because the
spatial coherence of the wavefront is not
H
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preserved. However, very many techniques
are still valid if the physical character-
istics of the screen are properly considered.
Of these the size of the irregularities
producing the scattering is the most
important. Some techniques are highly
sensitive to these while others are not.
The influence of nonuniform illumination
across the observing optics was investigated.
The specific influence depends upon the scattered
intensity distribution and also very much on
the specific details of the viewing system.
Scanning and additional electronic processing
can yield directly the resolution characteristics
of a screen or complete display system.
This study has shown the applicability of
conventional resolution theory to light
scattering display media and also has uncovered
many interesting topics to be given further
study in the theoretical and experimental phases
of the program. This study of screen resolution
will also be included as part of the interim
report.
3. Familiarization with Corning Manufacturing Facilities
A trip to our facilities at Corning, New York, was
made during this period. Many technologies applicable
to the manufacture of rear projection screens were
seen and discussed with various research personnel
from a number of different departments.
Five major classes of materials to be investigated
in detail are:
A. Glass Ceramics
Glass ceramics are materials that have been
converted into crystalline ceramics from
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their original glassy state by the use of
nucleating agents and heat treatment. A
glass batch containing a suitable nucleating
agent is melted and formed into a transparent
glass by conventional glassmaking techniques.
It is then cooled to temperatures inducing
precipitation of the nucleating agents.
Then, the nucleated material is heated to a
temperature range in which growth of the
nucleated crystals takes place and where
typical crystal size is .1 to .3 microns.
Composition of the material and degree of
heat treatment determine the type of
crystallization and final properties such
as its translucency and scattering properties.
Three different samples of this material have
been obtained.
B. Photosensitive Glasses
Photosensitive glass when exposed to ultra-
violet light and heat behaves much like a
photographic film or paper. An image is formed
that is a permanent part of the glass and
extends in depth throughout the body of the
glass. Exposed ?areas turn an opalescent white
after development by a heat treatment. The
unexposed areas remain clear. Thus, any
pattern can be reproduced in this glass by
exposing and developing it. Screens containing
over 350,000 precisely-located holes per square
inch are produced by this technique. This
material is known by the trademark "Fotoform".
The Fotoform glasses can be converted by
further heat treatment into a crystalline ceramic
material. In this state the material can be
translucent or opaque depending on how it is
treated and it is mechanically harder and stronger
than it was in the glassy state. It is marketed
under the trademark "Fotoceram".
?I
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C. Multiform Glasses
These are formed by powdering a glass, pressing
or slip casting the particles to shape and then
firing at a high temperature. The particles
are consolidated or sintered by fusion into a
vacuum-tight structure.
Multiform products display properties similar
to those of
the size of
temperature
glasses can
the parent glass. By controlling
the glass particles, the firing
and the firing time, multiform
be made to have a wide variety of
light scattering characteristics. The normal
particle
small as
also can
particle
size is 5 microns but canbe made as
3 microns with no large size limit and
be made with a given distribution of
sizes.
D. Porous Glasses
These glasses are composed of two different
glasses with one being
than the other. After
formed it is placed in
out the soluable'glass
skeleton. The size of
very much more soluable
the glass has been
a solution which leaches
leaving a very porous
pores range from 10
Angstroms to 500 Angstroms. This gives the
material a milky look but they eventually
discolor because of the collection of organic
substance in the pores. This can be avoided
by covering the surfaces with a resin or similiar
sealing material. The porous glasses can be
made more translucent by filling the pores with
an opalizing agent, the concentration of which
can be varied to change the translucent
properties to suit a particular application.
We have one sample of this material and expect
more in the near future.
7g/7,77p
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E. Optical Fibers and Matrices
Reference is made to discussions in previous
reports and elsewhere in this one and will not
be considered further here.
4. Progress on Rear View Screen Materials
A. Manufacture of Hollow Fibers and Matrices
As earlier reported, we are considering the
feasibility of using hollow fibers which have
been assembled into a matrix as a rear
projection screen material. The group working
in the Television Products, Market Development
Department at Corning, New York, has made such
hollow tubes down to 10 microns in inside
diameter with good control of open area to
wall area. In the 10 - 20 micron diameter
region this can be as much as 70/30. At smaller
diameters, wall thickness remains constant but
the hole gets smaller and smaller until it becomes
a solid fiber. This may be the most difficult
material, at least initially, to obtain samples
of as they must be made specially to order and
can be of any desired shape both inside and
outside. We can obtain samples by December
consisting of a matrix of 10 - 20 micron diameter
hollow fibers measuring up to 2" x 2".
B. Metalizing of Hollow Fiber Cores
At present the Advanced Products Department of
the Technical Products Division at our Corning,
New York, facility is attempting to coat the
inside of hollow fibers using a new type of
coating material from Hanovia. This is a
mixture of solvents, organic compounds, and
metallic salts. After a coating of this the
fibers are fired which breaks up the organic
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material and creates a reducing atmosphere
leaving a fresh metallic coating on the
fiber. All wastes becomes trapped in the
vapor and are vented off. Many of the
popular plating materials can be handled
in this way. This is expected to give us
an early estimate of the feasibility of
plating both fibers and matrices in this
fashion and also gives an estimate of the
requirements, in terms of time and facilities
to do this type of work if it proves successful.
The results of this effort are expected next
period.
C. Losses in an.UncoatedHollLGlass Fiber
A theoretical study was made to determine the
transmission losses through a hollow uncoated
opaque glass fiber.
The loss of power through such a fiber is due
primarily to penetration of energy through
the inner fiber wall. This is either absorbed
if the fiber is not clear or else it is simply
refracted out of the fiber and into the
surrounding media.
The power penetrating the walls of the fiber as
a function of incident angle 0 and refractive index
n of the wall relative to the hollow core, for
two orthogonal polarizations is given by the
familiar Fresnel equations.
,
parallel /Li (0) = Tan2 Ce
normal / n (e) = Sin2 (e
(0 +0)
Ce +0)
(1)
(2)
where IP(A), 7;1(0) are the transmission coefficients
for the electric vector parallel and normal to the
plane of incidence respectively, and 0 is the angle?
of refraction given by Snell's law,
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13 teadZh:',&,1
-1 Sin e,
= in ( )
(3)
The reflection coefficients R (0) and Rn (0) are
simply
R (e ) = 1 i (0)
Rn(e) = ? Tn(e)
For the Molybdenum impregnated glass all energy
which passes through the first wall is absorbed
hence R (0) and Rn (0) are valid reflection
coefficients and describe the losses per reflection.
For a clear non-absorbing glass fiber only a few
percent of the energy incident at a point on the
wall will be returned to the hollow core by
reflection from the second wall if it is uncoated.
Because total internal reflection is no longer
responsible for the propagation of light down the
fiber the numerical aperture must be given in terms
of the angle at which the transmission coefficient
T(e,r) falls below some predetermined value.
It should be mentioned that a black glass is not
necessarily more reflective than one which is clear.
The contrast of the image in the black glass is
much higher and subjectively influences the
observer's evaluation of the reflected image
seen. However absorbing glasses prevent cross-talk
between fibers when used in a matrix.
The total loss of power at a given angle of
incidence is determined by the length of the fiber,
i. e., the number of reflection and the reflectivity.
The number of reflections in a fiber of length Lo
and diameter d, r = 42, as a function of 0 = 90-e
is found from the geometry of Figure 1 to be,
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. ' r -9-raT 1,-..,.?.
f, 'il,,
).j ti'ft [4.
N(e,r) = r Tane ' (6)
Therefore the total transmission coefficient
T(0,r) for the fiber becomes,
,(0
T (e,r) = R (e)N r)
Tn(e,r) = Rn(0)
writing (7) and (8) out,
(7)
N(e, r) (8)
Tan2(e+95)
Tan2(01 r Tan 8
r Tan 0
Sin2 (el
sin2 (e+95)
(9)
(10)
It is clear from (9) and (10) the losses are compounded
as 0, increases. This is because both the reflection
coefficient decreases and the number of reflections
increases with increasing 0'.
One measure of the transmission properties through
such fibers is the number of reflection n required
to reduce the transmission coefficient to some given
0j40t-
,
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value. As an example Figure 2 gives n as
function of the angle 0 to reduce the trans-
mission coefficient to .01. It is clear, even
at large angles that only a very few reflections
are required. It should be noted in using
Figure 2, n must be integer. An equivalent measure
is the ratio Lo /d, for which the transmission
coefficient drops to .01 and is shown in Figure 3.
Consider what these means in terms of fiber diameter,
length, and angle of incidence.
The maximum length of a fiber with a diameter of
50 microns at 0 = 75?; is .9 mm for the parallel
component which undergoes 5 reflections and .4 mm
for the normal component which reflects twice.
It should be remembered each polarization is being
considered independently. In view of the data
given in Figures 2 and 3 and this example, it
seems impractical to consider uncoated hollow
fibers as a component for rear projection screens
because of their high losses.
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value. As an example Figure 2 gives n as
function of the angle 0 to reduce the trans-
mission coefficient to .01. It is clear, even
at large angles that only a very few reflections
are required. It should be noted in using
Figure 2, n must be integer. An equivalent measure
is the ratio Lo /d, for which the transmission
coefficient drops to .01 and is shown in Figure 3.
Consider what these means in terms of fiber diameter,
length, and angle of incidence.
The maximum length of a fiber with a diameter of
50 microns at 0 = 75?; is .9 mm for the parallel
component which undergoes 5 reflections and .4 mm
for the normal component which reflects twice.
It should be remembered each polarization is being
considered independently. In view of the data
given in Figures 2 and 3 and this example, it
seems impractical to consider uncoated hollow
fibers as a component for rear projection screens
because of their high losses.
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