The T1 light valve remained in production in monochrome, two-color, and three-color versions, essentially unchanged from the first experimental units in 1958 until the business was shut down in 1994. General Electric sold its Talaria business along with its defense business to Martin Marietta in 1993.12 which in turn sold the Talaria business to NEC in 1994. Like the Eidophor, the Talaria was unable to handle the competition from LCD projection systems such as the Barco Light Cannon and went out of production shortly after the sale to NEC. While no Eidophor projectors are believed to be operable today, functioning Talaria with its sealed light valve still remain in service. Due to the very high operating cost for a Talaria (estimated in 1992 to be about $100 per hour), plus the difficulty in getting service and replacement parts,13 it is believed that the Talaria remaining in service today are targeted for replacement. For example, in 2006, the Dutch National Aerospace Laboratory replaced the Talarias in its F-16 pilot-training simulator with Barco SIM6 Ultra II projectors.14 The Barco press release said its projector represented "an ideal replacement for the end-of-life Talaria projectors because they fit perfectly with the complex existing configuration."
CRT Projectors in the Post-War Years
Research and development into CRT projection systems continued through World War II. In the post-war years, a number of CRT projectors were installed in theaters. In 1948, RCA demonstrated a balcony-mounted projector that used a 15-in. CRT with an anode voltage of 80 kV, as shown in Fig. 8. The Schmidt-type optical system consisted of a 500-lb. 42-in. mirror with a 36-in. lens.
By 1951, there were about 100 theater projector installations, with RCA having about a 75% market share. That year, there were about 300 live shows transmitted. For example, in 1952 the Opera "Carmen" was cinema-cast in black-and-white live from the Metropolitan Opera in New York to movie theaters in 27 cities.
Color CRT projection systems have almost always used three CRTs. Figure 9 shows a 1951 color CRT theater projector specifically designed to receive the simultaneous color video signal proposed by RCA that was eventually adopted as the NTSC color standard.15
The consumer was not ignored by the CRT projection business. CRT projectors were sold, or at least offered for sale, to consumers interested in images larger than the direct-view televisions of the time could produce. Figure 1016 shows a 1951 advertisement for a TV projector for £146.15. At an exchange rate of $5/£, this is a total of $734.
In the 1950s and 1960s, the interest in CRT projection systems declined for large-screen applications because they could not compete with light-valve projectors such as the Eidophor and Talaria. The consumer-electronics industry produced direct-view CRTs in larger and larger sizes, reducing the need for projection systems. During this period, the CRT projector was mostly limited to professional applications where the screens were not large enough to justify the use of a light-valve projector.
The lull in consumer CRT projectors ended in 1972 with the introduction of the Advent VideoBeam projector with Schmidt optics, developed by Henry Kloss from a design by Art Tucker.17 In the Tucker and Kloss designs, the Schmidt mirror was inside the CRT vacuum-tube envelope. While this ensured the mirror remained clean, it lead to a very expensive CRT. This cost was acceptable in a military simulator where the alternative at the time would have been an oil-film light valve, but a difficult sell in the consumer market.
The VideoBeam was a two-piece three-CRT system housed in a coffee-table-sized console with the picture projected on a 7-ft.-diagonal curved aluminized screen that had to be placed precisely 8 ft. away. Kloss left Advent in 1976 and founded Kloss Video, where he built the NovaBeam series of CRT projectors of similar design to the VideoBeam. Again, the high prices of the Advent and Kloss Video systems prevented widespread sales, and Advent went bankrupt in 1981. Kloss Video was eventually bought by Ampro.
While at the time, Kloss got much of the publicity, other companies introduced CRT front projectors of a more conventional design. In 1972, for example, Sony also introduced its popular VPH series of CRT projectors intended primarily for professional applications. These continue to be popular with home-theater enthusiasts to this day.
Consumer-electronics manufacturers concentrated on CRT projection systems in the years following the re-introduction of consumer projection by Kloss, Sony, and others. Products included two-piece front-projection systems such as the Advent 760; one-piece front-projectors such as the Advent VB125, Sony KP-5000 and Quasar PR6800QW; and one-piece rear-projection systems such as Quasar CT-4500 "CinemaVision" with a 45-in. screen. The sales of large-screen consumer systems was spurred, in part, by the introduction of Beta and VHS videotape systems in 1976. While the Sony Beta system initially only had a 1-hour capacity, the JVC VHS system introduced only months after Beta had up to 2 hours of capacity. This made most films available in prerecorded form, and consumers wanted to watch these films on large screens.
Fig. 8: 1948 RCA Monochrome CRT Projector for Theatrical Use with a 15" CRT and 42" Schmidt Optics (Photo courtesy of Radio Age)
Two key product introductions in 1979 enabled the rapid growth of the rear-projection TV business. The first was the f/1.0 projection lens from U.S. Precision Lens. This extremely low f/# allowed the collection of enough light to make an image of sufficient brightness. While a f/1.0 refractive lens did not collect as much light as af/0.7 mirror in the Schmidt optical system used by Advent and Kloss video, it cost much less and produced enough light when a relatively high-gain rear-projection screen was used. By the 1980s, these lenses were typically liquid coupled in a process originally developed for military CRTs. This increased the brightness at the screen by cooling the tube, allowing higher powers. The elimination of the air space also eliminated reflections and increased brightness and contrast.
A liquid-coupled CRT projection lens is shown in Fig. 11.18 While this particular design comes from USPL near the end of the CRT projection business, it has design features common with all liquid-coupled lenses. The liquid was contained between the CRT faceplate and a deeply curved thin element. This lens element/liquid combination formed a strong negative lens near the image plane. The effect of this lens was to correct the field curvature of the lens/faceplate combination so the image could be focused on the flat projection screen, a problem discussed by Wolf in 1937. This design has five elements but other designs had either four or six elements, depending on the vintage and the quality of the image to be produced. Typically, one of the elements would have most of the power in the lens, L2 in Fig. 11, while the other elements served to correct aberrations introduced by this strong wide-field-of-view low-f/# element.
The second enabling product was the development of the color-corrected lenticular projection screen commercialized by Freen Screen. Rear-projection screens based on Fresnel lenses had been around since 1940.19 These screens were intended to have the image source on axis and were not suitable for use in high-gain three-CRT rear-projection designs. This problem was solved with the invention of a color-correcting screen in 1970.20 This color-correcting screen allowed the use of off-axis CRTs in relatively high-gain screen applications. With previous high-gain screen designs, the on- and off-axis CRTs produced angular light distributions that differed from each other, leading to color shifts for viewers that were not on the centerline of the screen.
While growth in consumer CRT rear-projection systems continued through the 1980s and 1990s, professional CRT projectors felt the same pressure from LCD, DLP, and LCoS systems that had doomed the Talaria and Eidophor, especially at lower resolutions. For example, in the 1998 projection shoot-out at Infocomm,21 there were only six CRT projectors in the VGA, SVGA, and XGA categories. In the high-resolution 1280 x 1024/1600 x 1200 section, there were four CRT projectors, and only a single LCD projector, from ASK.
Hughes/JVC ILA projectors
The Hughes Light Amplifier LCD technology began at the Hughes Aircraft Research Labs (HRL) in Malibu, California, in the 1970s. Solid-state physicist W. P. Bleha and liquid-crystal scientists J. D. Margerum and A. M. Lackner developed a photoconductor/liquid-crystal image spatial light modulator. While the original intention had been to develop an optical signal-processing system for use with lasers, another HRL development, the value of the system as a display was recognized. In a display application, the photoconductor was driven by an image generated on a CRT and relayed to the photoconductor surface. The spatial variation of the conductivity of the photoconductor changed the spatial voltage distribution on the liquid crystal. This in turn spatially changed the liquid-crystal orientation and controlled the polarization of the light from an external lamp. This use of a dim CRT image to control a very bright image at the screen led to the phrase "Light Amplifier," although at the time the technology was more commonly known as a liquid-crystal light valve (LCLV). By 1972,22 this system had shown sufficient image quality to interest the U.S. Navy in the use of the system for a shipboard display. A full-color version of the projector suitable for television was developed by 1977.23 Production of the LCLV began for the U.S. Navy and Air Force began in the early 1980s.
Fig. 9: RCA Tri-color receiver-projector, which provides theater-size screen images, is shown with its developer, Dr. David Epstein (Photo courtesy of David Sarnoff Library, Princeton, NJ)
In the 1980s, Hughes continued to develop the technology and developed the second-generation LCLV, based on an amorphous-silicon photoconductor. The higher speed of silicon allowed full-motion high-resolution video images to be displayed. In addition, the homeotropic alignment of the liquid crystal was stabilized leading to substantially improved contrast ratio over the hybrid field-effect mode that had been used in the first-generation Hughes LCLV.
Interest in LCLVs was not limited to Hughes. For example, the November 15, 1989 special issue of Applied Optics had 26 papers on spatial light modulators, most of them based on liquid crystals. The 89 authors of these papers included representatives of 30 different institutions, including of course, Hughes and Texas Instruments. Several of the institutions were represented by several papers. One of the papers,24 while not intended as a review paper, had a massive bibliography of 89 references.
Hughes Aircraft Co., recognizing the future commercial importance of this display, spun off the LCLV activities into a subsidiary, Light Valve Products, Inc., in 1989. At this time, the LCLV was given the trademarked name ILA or Image Light Amplifier. Soon Light Valve Products, Inc., was demonstrating large-screen displays for digital cinema in Hollywood and large-venue applications.
In 1992, Hughes and JVC formed a joint venture, the Hughes-JVC Technology Corp. (HJT), to produce ILA projectors and take advantage of the global JVC operations. From 1992 to 2000, HJT shipped over 3500 ILA projectors into large-venue applications around the world. In June 1999,25 two 12,000-lm ILA projectors from HJT were used for the world's first demonstration of digital cinema to paying customers when Star Wars Episode 1 was shown in Los Angeles and New York. The projectors used were similar to the one shown in Fig. 12. Simultaneously, DLP projectors from Texas Instruments showed the same movie in two other theaters, also in Los Angeles and New York.
Fig. 10: British advertisement for a CRT projection system in 1951 from the Daily Mail "Guide to Television."
HJT worked with JVC to develop the D-ILA microdisplay, which was launched in 1997. In this system, the LC drive voltage produced by the a-Si photoconductor was replaced by a voltage drive from an active-matrix silicon backplane. This eliminated the bulky, troublesome, and expensive CRT used to generate the image. This significantly reduced the size of the panels and the optical system. Although single-lens ILA projectors had been built,26 their performance was not fully satisfactory compared to the three-lens versions. The smaller size of the D-ILA panel not only allowed single-lens operation but it enabled the development of consumer versions of the D-ILA system. Improvements in optical components and architectures were also instrumental in the development of single-lens LCoS projectors.
In the next installment of this article, in the August issue of Information Display, we will continue the chronology and explore how the development of LCOS, DLP, and LCD technologies threatened the dominance of light valves and CRTs as the industry of projection displays took on the period from the 1990s to the 2000s.
References
1W. H. Priess, "Mechanical vs. cathode television systems," Radio-Craft, 79 (August 1936).
2F. Okolicsanyi, "The wave-slot, an optical television system," Wireless Engineering 14, 526 (1937).
3W. E. Shrage, "The balance sheet of televi-sion," Radio-Craft 9, No. 2, 80 (August 1937).
4"The projection kinescope makes its debut," Radio-Craft 83 (August 1937).
5M. Wolf, "The enlarged projection of television pictures," Philips Technical Review 2, No. 8, 249–253 (August 1937). Gain and viewing angle were estimated by MSB by scaling from the drawings in the paper.
6Lux is a measure of illuminance and is not used in modern reports of projector output. Presumably, Wolf measured the illuminance provided by the CRT projection system at theimage plane with the projection screen removed.
7H. Johannes, The History of the EIDOPHOR Large Screen Television Projector (Gretag Aktiengesellschaft, 1989), p. 110.
8Interview with Phillipe Roth, optical specialist in the R&D Lab Systems Division of Gretag Imaging, as reported in http://www. spgv.com/columns/eidophor.html.
9 http://www.cinephoto.co.uk/eidophor.htm.
10W. E. Glenn, "New color projection system," J. Opt. Soc. Am. 48, 841–843 (1958).
1 T. T. True, "High-performance video projector using two oil-film light valves," SID Symposium Digest Tech Papers 18, 68–71 (1987).
12General Electric 1993 Annual Report.
13Replacement Talaria parts including light valves are still available from Vacuum Optics, http://www.vacuumoptics.com/.
14Barco Press release, "Barco brings fresh light and vision to Dutch National Aerospace Laboratory NLR" (11 December 2006); http://www.barco.com/corporate/en/press releases/show.asp?index=1860.
15The Story of Television (Radio Corporation of America, 1951).
16F. Coven, ed., Television Guide (Daily Mail, London, 1953), p. 128.
17W. E. Good, "Projection television," Proc SID 17, No. 1, 3–7 (1976).
18J. Moskovich, "High performance projection television lens systems," U.S. Patent 6,509,937, Issued January 21, 2003 and assigned to U.S. Precision Lens.
19J. D. Strong and R. Hayward, "Transparent projection screen," U.S. Patent 2,200,646, Issued May 14, 1940.
20W. E. Glenn, Jr. (Assigned to GE), "Composite back projection screen," U.S. 3,523,717, Issued August 11, 1970.
21P. H. Putman, Infocomm '98: A Review (1998); http://www.digitalcontentproducer. com/mag/avinstall_infocoreview_2/index. html.
22 A. D. Jacobson, W. P. Bleha, Jr., D. D. Boswell, M. Braunstein, J. D. Margerum, and S-Y. Wong, "Photo-activated liquid crystal light valve," SID Symposium Digest Tech Papers 3, 70 (1972).
Fig. 11: High-Performance, Liquid Coupled CRT Projection Lens from U. S. Precision Lens
23A. D. Jacobson, D. O. Boswell, J. Grinberg, W. P. Bleha, P. G. Reif, B. Hong, S. Lunquist, and J. Colles, "A new color TV projector," SID Symposium Digest Tech Papers 3, 106 (1977).
24K. M. Johnson and G. Moddel, "Motivations for using ferroelectric liquid crystal spatial light modulators in neurocomputing," Appl. Opt. 28, No. 22, 4888–4899 (1989).
25R. D. Sterling and W. P. Bleha, "D-ILA technology for electronic cinema," SID Symposium Digest Tech Papers 31, 310 (2000).
26A. G. Ledebuhr, "Full-color single-projection-lens liquid-crystal light valve projector," SID Symposium Digest Tech Papers 17, 379–382 (1986). •
Fig. 12: Hughes/JVC 12K projector used in 1999 digital-cinema tests.
Matthew Brennesholtz is Senior Analyst at Insight Media, 3 Morgan Ave., Norwalk, CT 06851; telephone 203/832-8464, e-mail: matthew@insightmedia.info.