IMPROVED SCREEN FOR REAR PROJECTION VIEWERS

• Document Type: CREST
• Collection: NGA Records (Formerly NIMA)
• Document Number (FOIA) /ESDN (CREST): CIA-RDP79B00873A002000010082-2
• Release Decision: RIPPUB
• Original Classification: C
• Document Page Count: 10
• Document Creation Date: December 28, 2016
• Document Release Date: November 8, 2012
• Sequence Number: 82
• Publication Date: July 11, 1966
• Content Type: REPORT

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ENTEDENTIIM
CORNING GLASS WORKS
ELECTRO-OPTICS LABORATORY
RALEIGH,, NORTH CAROLINA
IMPROVED SCREEN FOR REAR PROJECTION VIEWERS
technical Report No. - 11
Date - July 11, 1966
Period Covered - May 27, 1966
to
July 11, 1966
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THE NATiONAL DEFENSE OF THE UNITED STAT, VVETNEES
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ABSTRACT
This report summarizes the first results of preliminary
investigations on glass-ceramic and Fotoform samples.
Two samples were found to give an axial gain of 2. and
still meet the criteria for brightness uniformity. A
program to determine the physical properties of these samples
as to their particle size, relative refractive index, and
number density is outlined. Some preliminary sine-wave
resolution masks have been made. The status of this
effort along with a completion schedule of the MTF analyzer
is given.
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TECHNICAL REPORT NO. 11
1. Materials Investigation
A. Glass-Ceramics
A large number of glass-ceramic materials containing
different particle size and volume density have been
ground and polished. After preliminary testing, seven
of the most promising samples were measured in the
goniophotometer. The results are given in Figure 1
which shows the angular gain function versus the
scattering angle.
Some of the samples, mainly AC16C, AC18A, AC19A, and
AC19B, give very uniform screens but have correspond-
ingly low efficiencies because of multiple scattering,
Table I. The diffuse transmittance is the fraction
of light scattered into the forward hemisphere. The
I45/I0 column is the fraction of incident light
scattered inside ?45?. The thicker the sample, the
greater the probability of multiple scattering
occurring as can be seen by comparing the gain curves
of identical materials of different thickness, i. e.,
comparing AC16A with AC16C, AC18A with AC18B, and
AC19A with AC19B. The first two pairs show a change
in the shape of the scattering function with thickness,
which implies the order of scattering has changed.
This does not happen with the last pair indicating
that, even at the smaller thickness, the particle den-
sity is high enough so that high-order multiple
scattering still dominates. If this sample were cut
still thinner, the scattering curve would probably
show a maximum at 0 = 0, similar to AC18B. These
comparisons clearly indicate that optimization of
a material is important and can give a significant
improvement in its light-scattering characteristics.
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TABLE I
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Summary of Optical Properties of the First OGW Samples
Sample
Diffuse Transmittance
%"
Diffuse Reflectance
145/10
Gain
(9=0)
Thickness
(mm)
AC16A
67
27
46
1.9
.366
AC16C
61
39
36
1.4
.864
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51
49
30
1.2
.861
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70
30
44
2.0
.345
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39
61
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.9
.853
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62
38
34
1.5
.366
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39
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Efficiency versus axial gain (0 = 0) is plotted in
Figure 2 and compared with values predicted from
single scattering theory. The cluster of data around
the M = co line indicates that multiple scattering
dominates, rather than implying the relative index
of refraction of the particles is infinite.
The best samples over all are AC16A and patticu1arly
ACM. Their variation in brightflesth.?1:1%.,
and +14% respectively, both less than the maximum
tolerance of +15%. Here the variation in brightness
is computed from the relation
Gain (0?) - Gain (45?)
Variation in Brightness -
Gain (0?) + Gain (45?)
A detailed analysis of particle size, refractive index,
and number density of these samples is being made.
Electron micrographs will identify the particle geometry.
The other samples which have been ground and polished
will be measured, and the remainder of the better
original samples will be ground, polished, and tested.
B. FotoformR Glass
An investigation of FotoformR glass has been initiated.
Some promising materials have been obtained by not
exposing the samples to ultraviolet light and by
regulating the crystal growth with the time-temperature
development cycle. We have found this produces a layer
of crystalline material which is confined to the surface of
the glass. The thickness of this layer has been correlated
very well with temperature. Samples with crystalline
layers from 10 microns to 500 microns have been obtained
and are presently being prepared for optical evaluation.
Following this, practical-sized screen samples for visual
evaluation measuring 3" x 3" will be made using those
heat treatments which result in optimum optical properties.
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Studies using different exposures together with
different heat treatments are presently being
carried out. We are also preparing to form lenticules
on the surface of this material by exposing it through
fine masks and by leaching away part of the glass.
C. Lenticular Surfaces
Samples of solid, spherical glass beads have been
obtained which range in size from 65 microns to 325
microns. These, along with the cylindrical lenticular
film, will.be used for investigating lenticular
surfaces.
2. Instrumentation
A. Goniophotometer
A refractometer was used to measure several solutions
to determine their refractive index for use in the
liquid sample cell of the goniophotometer. Several
laboratory solvents were measured and all had refractive
indices well below that of glass, which generally ranges
between 1.47 and 1.52. Sugar in water, one of the better
solutions, gave refractive indices between 1.33 and 1.48
at room temperature. Data were taken on the refractive
index as a function of percent sugar, by weight. It
was found that stock solutions can be made in this way
with an accuracy of better than 0.2%, without requiring
a refractometer. Solutions with n greater than 1.45
have very small crystals suspended in them which produce
some undesirable scattering. Cinnamon oil had the
highest refractive index measured, 1.605. This can be
diluted with acetone down to n less than 1.4. The
solution is somewhat yellow, but relatively nonvolatile.
This mixture or a diluted refractive index oil will
finally be used.
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B. MTF Analyzer and Sine-Wave Mask Generator
The unit has been set up to make sine-wave masks,
and the system has been checked out. Several masks
have been made, one of which is shown in Figure 3.
These have spatial frequencies from 0.2 to 10 lines/mm,
a ratio of 50:1. The spatial frequency has been shown
to increase linearly with distance along the mask.
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Figure 3. A Typical Sine-Wave Resolution Target
There is sufficient light energy through the 10-micron
slit, which is in contact with the film, to give the
necessary densities. We have used a rotating polarizer
in a collimated,polarized beam as the light modulator.
This works quite well and no difficulties have been
encountered with this unit. We are slightly modifying
the film transport unit so that it will run smoother and
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not produce differences in exposure along the film.
The photodetector unit for use in the MTF configur-
ation and for measuring the sine-wave masks has been
completed and is working.
Dust in the slit, which is attracted to the film by
static electricity, has been a problem. We have
found that to prevent clogging of the slit and
streaking of the film, the slit must be flushed with
antistatic film cleaner and left to dry by evapor-
ation each time before making a mask. We are also
modifying the slit so that a stream of air will pass
between it and the film. This we hope will keep the
slit completely open by removing dust from the film
before it passes in front of the slit. Final masks
are expected within the next month.
Design of the "contrast computer" has been set; all
necessary components are presently being ordered.
Assembly is scheduled to begin by August 1 and com-
pletion is expected by September 1. Until then we
will use an oscilloscope to collect MTF data on the
more promising samples.
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