Prepare yourself for the ultimate adventure through time and space, from the comfort of a reclining seat inside a domed theater. Planetarium shows never fail to deliver awe and wonder to people of all ages and backgrounds. At the center of many planetarium theaters is a projector. While a lot of these awe-inspiring shows are now digital, there are few machines in the world that are as beautiful, quirky, complex, and awe-inspiring as the optical-mechanical planetarium (OM) projector. The OM planetarium has all the motorized intricacies and curiosities of a mechanical wristwatch coupled to truly high-end optical lenses that, in some cases, are identical to those attached to the front of your camera. These machines are true works of art, not only in their designs, but also in the precision of their faithful recreations of the night skies above. Do these machines have a future in today’s digital age? Well, in the world of planetarium projectors, the digital vs. analog (vs. hybrid) debate is alive and well to many who design, operate, and upgrade their dome theaters.
Photographs © Todd Vorenkamp unless otherwise noted
Background:
I have two clear memories of third grade. I got a LEGO fire station for my birthday and I fell in love with Stella. She was possibly my first love. I met Stella on a field trip to the Children’s Museum in West Hartford, when I walked into the planetarium and saw her in the middle of the room—the center of attention. I remember nothing about the planetarium show I saw that day, but all these years later, I can still visualize Stella—the Spitz Transit Projector that projected more than 4,000 stars on the dome. [Fun fact: A Spitz STP was operated in a New York City nightclub for a time.] I remember looking at Stella more than I did the stars projected overhead. What a wonderful machine she was—glowing domes at the end of the device, and everything seemed to be in motion in and around the projector. This has led to a lifelong fascination with planetarium projection systems.
As a photographer, I was surprised when, several years ago, I noticed the beautiful Zeiss IV—a planetarium projector at the National Air & Space Museum’s Einstein Planetarium—was equipped with Zeiss P-Planar 112mm f/2.5 enlarging lenses. With this discovery, I realized that the projectors of my dreams were equipped with optics from the world of photography.
And, in case you were wondering how my love affair worked out, Stella was retired by the museum in 2007, and the Travelers Science Dome at the Gengras Planetarium now uses a Spitz SciDome HB digital projection system. Luckily, Stella is enjoying her retirement at the Planetarium Projector Museum in Bear Lake, California, under the watchful eye of director Owen Phairis.
A Brief History
A planetarium is, by definition, a device that shows a model of the cosmos. Early planetaria included desktop mechanical models of the solar system (as it was known at the time), known as an orrery, named for its inventor, the Irish Earl of Orrery, who made one in 1712. These planetariums expanded to more intricate physical models—some that filled rooms. Some mockups of the heavens were painted inside of small, portable domes. Visitors could go inside and see a representation of the heavens above. Some mechanical clocks contained complex celestial models like the Prague Astronomical Clock (or Prague Orloj) that still operates today. Today, the most common planetarium is a large (or small) domed theater with a planetarium projection system inside.
Following the development of the first OM planetarium projector, by Zeiss, in 1923 [more on the Zeiss Model 1 below], domed planetaria started popping up around the globe. Through the 1920s and 1930s, before the start of World War II, there were 25 planetariums featuring (OM) star projectors. Locations included Germany, which had five. Ten others were spread throughout the rest of Europe. The United States also had five: Adler Planetarium, in Chicago (built in 1930—America’s first planetarium); Fels Planetarium, at the Franklin Institute, in Philadelphia; the Griffith Observatory Planetarium, in Los Angeles (now called the Samuel Oschin Planetarium); Buhl Planetarium, at the Carnegie Science Center, in Pittsburgh; and the American Museum of Natural History’s Hayden Planetarium, in New York City.
Planetariums continued to expand and, in the 1960s, the world welcomed the “Space Race” and, along with it, a new interest in the heavens. This spurred the development of digital technologies, including digital special effects (SFX) for film and television. The optical effects and digital planetarium maker Sky-Skan started developing SFX projectors, in 1967, to augment the OM projectors in planetariums with other celestial phenomena.
Auxiliary slide projectors were used in conjunction with the star projector for the first “hybrid” planetarium programs. Some planetariums employed upwards of 100 auxiliary projection systems. Visitors to these domes may recall the sound of dozens and dozens of slide projectors clicking and then resetting around the room. Many planetarium projector manufacturers, as well as the planetarium staffs themselves, created specialized SFX projectors to display different visuals, such as the one visible galaxy—Andromeda—shooting “stars,” comets, and other celestial phenomena. Development of the desktop computer system offered advances in projector control, allowing special effects projectors to synchronize automatically with optical projection shows, to further facilitate programmed presentations.
In 1983, Evans & Sutherland, the “world’s first computer graphics company,” created Digistar—the first digital planetarium system. The first E&S Digistar used vector graphics which rendered stars as blurry blobs with fuzzy edges—not the crisp points of light that the OM projectors had perfected over the decades. Regardless of the rudimentary visuals, the planetarium had now moved into the world of computer-generated imagery (CGI) and, with it, the ability to “fly” through the stars in a simulated three-dimensional cosmos.
The mainstream arrival of large-format film IMAX theaters (both domed and flat screens) in the 1970’s also served as a catalyst for change in the world of planetarium programs and design. The lure of new CGI and digital projection and, separately, the immersive nature of IMAX, was stealing the visual thunder of the traditional OM star field planetarium. To compete, planetariums began to include video projection onto their domes. Now planetarium visitors could watch a video of a star go supernova, a galaxy spiral, and other stellar events. At first, a single video projector might show a motion picture at some point in the program. Before long, multiple projectors were placed into use. And, eventually, computer technology allowed for the blending of multiple projectors to create a single large image. In 1997, digital blending of multiple projections was combined with optical technology to create Sky-Skan’s SkyVision, a full-dome digital projection system that went live in Houston’s Baker Planetarium, in 1998.
By the end of the 20th Century, the world of planetarium projection had split onto three distinct paths—traditional optical mechanical, digital full-dome projection, and hybrid combinations of digital and OM.
The Optical Mechanical Planetarium Projector
Described as “a confluence of two threads of technology—the astronomical clock [astrarium] and hollow globes” by John Stoke, Sky-Skan’s VP of Marketing and Sales, the first Zeiss OM planetarium projector, the Model I, was developed between 1919 and 1923. Zeiss’s Walther Bauersfeld developed the concept, but it took four years to convince Zeiss that his device had a future, and approve the build. According to Jon Elvert of ASH Enterprises, a company that maintains planetarium projectors around the word since 1971, the Zeiss Model 1 projector was a spherical design with 32 star projector condenser lenses “that collected light from a single lamp placed at the projector’s center. These early star plates were similar to slide transparencies, reproductions of star fields made from photographs taken of the real sky!” The projector was presented at the German Museum in Munich, on October 21, 1923.
The traditional OM planetarium projector, nicknamed “The Ant” due to its outward resemblance to the insect, consists of two large globes with a central light source in each dome. External to the main spheres are sun, moon, and planet “cages” that housed independent projectors for “the wanderers.” The Zeiss Model II, introduced in 1926, is the first dual-sphere ant-style projector, projecting almost 9,000 stars. For this model, tiny holes were drilled into the spheres in the precise positions of the stars above. Larger stars or groups of stars would get projection lenses to increase their brightness. Single-sphere projectors showed either the Northern or Southern Hemisphere, whereas dual-sphere ant-type projectors could show the sky in both hemispheres. To keep the spheres from projecting into the eyes of spectators, shutters mask the sky below the dome’s “horizon.”
Cost has long been a factor in the acquisition of an OM projector. The Zeiss Model II cost $75,000 in 1926—more than $1 million in today’s dollars. Modern OM projectors can cost well over $2 million.
Armand Spitz—a presenter at the Fels Planetarium—was captivated by the wondrous experience of the OM projector and felt that, because of the extreme expense of the systems, many people would never get to experience the magic of the artificial night sky. To spread the magic, he founded Spitz, Inc. and created the Spitz A-1, a 12-sided dodecahedron projector that retailed for only $500—well inside of the budgets of many small schools and educational institutions.
The optical-mechanical projector has always been renowned for its authentic representation of the night sky’s star field. Tiny bright dots mark hyper-accurate positions of our stars. Projected onto the flat gray surface of the dome in a dark room, the OM projector provides an unmatched simulation of the heavens—projecting thousands and, in some cases, millions of individual stars onto the dome overhead. The relative brightness and size of the stars are simulated and, adding to the realism of the artificial night sky, colored filters accurately portray the hue of different stars like red and blue giants. For added realism, some projectors even show artificial “twinkling” of the stars as if there was atmospheric turbulence between the seats and the planetarium’s domed surface!
The classic Spitz A3P projector was designed for domes 24-40' in diameter, with more than 1,000 units sold through the 1960s and 1970s. Still widely in use today by institutions like the Mystic Seaport Museum’s Treworgy Planetarium, in Connecticut, the A3P has 1,354 holes drilled into its star-ball, representing first- through fifth-magnitude stars. All first- and select second- and third-magnitude stars are projected through lenses to give the proper star brightness. The Milky Way is simulated with its own lens system. According to Treworgy Planetarium Supervisor Brian Koehler, "Our visitors are always telling us how amazed they are at the authenticity of our night sky. It seems many of them truly feel, when they sit beneath our A3P star field, like they are sitting out in a field somewhere looking up at the real stars." The City College of New York uses a slightly more complex Spitz 512 model, which is similar to the A3P design.
As good as the A3P is, more recent OM projectors show stars in the 1-7 magnitude range. Today’s Zeiss Model IX projects more than 9,000 stars, and the Zeiss StarMaster shows 9,100. Moving into the hundreds of thousands, the latest Konica Minolta projector shows 16,000-27,000 stars down to magnitude 7.5 and 380,000 stars in the Milky Way. Although the human eye cannot resolve the distant stars at the galactic core, the visual models designed by Japan’s Takayuki Ohira, for projectors like the Ohira Tech Megastar-IIA (using Canon EF 40mm f/2.8 STM lenses), shows a stunning representations of our home galaxy with millions of stars projected.
Marc Taylor, manager of Planetarium and Science Programs at New York’s Hudson River Museum, says that the traditional Zeiss projectors focus on the stars that Earthlings can see visually, while the Megastar-IIA does a better job of showing the “most realistic stars” of the Milky Way, instead of “fuzz bands” of stars displayed by projectors in the past. The latest Megastar projectors project more than 22 million stars—a Guinness World Record. This visual is designed for planetarium visitors to use binoculars to resolve the details!
Today, the “Ant” has generally been replaced by the star-ball-type OM planetarium projector. Instead of two hemispheric spheres at opposite ends of a long, mechanism-filled shaft, a single star-ball contains both hemispheres of stars in a spherical or egg-shaped unit. Harking back to the days of the geometrically shaped projectors, today’s Konica Minolta Infinium-L star-ball sports 20 hexagons and 12 pentagons as part of its award-winning body design. Projection technology has evolved from the shining of light through pinholes and lenses to using fiber-optic lines to transmit simulated starlight from the lamp to the surface of the star-ball. Light sources have also evolved from expensive, limited life, incandescent Zenon arc lamps to modern LED bulbs.
Projecting planets, the Sun, and the moon are usually jobs relegated to separate projection systems, as the position of these objects changes against the backdrop of the stars. These cages house auxiliary projectors and make up the main body of the “Ant,” or they live beneath single-sphere projectors. On modern star-balls, the cages often exist outside the star-ball in innovatively-engineered installations. Planetarium manufacturers also sometimes have the option of skipping out on auxiliary planetary projectors to reduce installation and maintenance costs.
Another factor in OM (and digital) projector employment is dome size. Steve Hatfield, Sales Manager/Consultant with Konica Minolta Planetarium Co., Ltd., says, “The majority of planetaria in the U.S. consist of small- to medium-sized domes whose diameters range from about 18' to 50'. Larger domes require both larger and brighter optical and digital projection systems.” For reference, the largest domed theater in the Western Hemisphere is the Jennifer Chalsty Planetarium at the Liberty Science Center, in New Jersey, which boasts an 89' dome. Planetarium No. 1, in St. Petersburg, Russia has a 121' dome—the world’s largest.
Digital Planetarium Projectors and Hybrid Planetariums
As mentioned above, once technology existed to blend computer-generated video projection, the full-dome digital planetarium became a reality. Evans & Sutherland demonstrated StarRider in 1996 at the Association of Science-Technology Centers conference and, in 1998, Sky-Skan’s SkyVision system launched. It consisted of six separate projectors—five horizontal surrounding the theater, and a single vertical projector pointed at the zenith of the dome, all of which were equipped with 35mm lenses.
Also noted above, the larger the dome, the more powerful the projectors must be. For example, New Jersey’s Chalsty Planetarium features 10 Christie Boxer projectors and a dome lighting system that produces 281 trillion (that is 281 followed by 12 zeros) colors. These 4K projectors each project 50 million pixels for a combined 88 million pixels—true 8K resolution—after blending. According to Mike Shanahan, director of the Liberty Science Center’s Jennifer Chalsty Planetarium, the projectors are “ganged together” through a large computer bank to provide “IMAX-like resolution.” Backing up the visuals is a 30,000-watt sound system with five speaker arrays and 16 subwoofers.
The Liberty Science Center welcomes 300,000 visitors a year to the Chalsty Planetarium and E&S Digistar 6 system. While their setup is extremely complex, luckily for smaller dome operators, producing a dome planetarium show does not always require such a massive size and large number of projectors and computers.
To that point, the Hudson River Museum, outside Yonkers, New York, features a hybrid system running a Sky-Skan digital system in conjunction with their Megastar. A pair of JVC D-ILA halogen-bulb projectors are tethered through four quad-core computers. The Cormack Planetarium at the Museum of Natural History in Providence, Rhode Island, shows Ash Warped Media digital shows in conjunction with their Zeiss ZKP 3 ant-type projector that, according to director and NASA Solar System Ambassador, Renée Gamba, is employed for every program. Many hybrid planetariums will forgo the OM projector, or just use it for certain programs. The Cormack’s OM projector has one of the oldest Zeiss projectors in operation in the US, and is regularly serviced by Zeiss technicians flown in from Germany.
Running in conjunction with their beautiful Zeiss Starmaster star-ball projector, the Boston Museum of Science projects Sky-Skan visuals through two Sony VPL-GTZ280 4K laser projectors.
In Centerport, New York, the Vanderbilt Museum’s Charles and Helen Reichert Planetarium also runs a hybrid system. At the center of the theater is a beautiful Konica Minolta Geministar III system featuring an Infinium-L projector incorporating fiber optics. The heaven’s 23 brightest stars are projected using 23 Konica Minolta lenses. On the digital side of the Geministar III system, Reichert planetarium director Dave Bush uses a pair of JVC DLASH7NLG projectors, each managed by four separate computers, which are then connected to blend the Sky-Skan Digital Sky II visuals created, in part, by the European Southern Observatory.
Evans & Sutherland has installed more than 35 hybrid systems around the world. Director of International Sales Scott Niskach says, “Today, no one would build a modern planetarium without a digital system included.”
Marc Horowitz, director of the Edwin P. Hubble Planetarium at the Edward R. Murrow High School, in Brooklyn, New York, runs a dual-projector system, which replaced their aging GOTO OM unit back in 2010. Running OpenSpace software (currently in development at the American Museum of Natural History, with Horowitz on the advisory board), installed by Elumenati, with Worldwide Telescope and Eyes on the Solar System as well as Uniview software, the planetarium features dual F35 4000-lumen LED projectors made by projectiondesign (now Barco), and Navitar Hemistar projection lenses.
And, for those small domes on a budget, a nearly full-dome digital experience can be had with a single projector shining onto a planar first-surface mirror and reflecting onto a first-surface spherical mirror, like the system being run at the City College of New York (CCNY) Planetarium, in Manhattan. Built in the basement of the Marshak Building, CCNY physics professor and planetarium director Dr. James Hedberg runs a Panasonic PT-RZ570 WUXGA 5400-lumen projector. The image reflects off the planar mirror up toward the spherical mirror, to cover approximately 90% of the dome; however, first surface mirrors are needed to prevent double-stars caused by reflections. Providence’s Cormack Planetarium also uses a single projector and spherical mirror.
Optical Mechanical? Digital? Hybrid?
The traditional OM projector allows viewers to enjoy a highly realistic star field, as viewed from the perspective of an observer on Earth. According to the Planetarium Projector and Science Museum’s Owen Phairis, “Digital is so much more versatile,” because it allows audiences to leave Earth and fly, virtually, anywhere in the known universe. Digital theaters can take audience members on nap-of-the-Mars flights through the canyons and valleys of the Red Planet, out to stellar nurseries where stars are being born, and to the event horizon of the black hole in the center of the Milky Way. As beautiful and amazing as an OM projector is, it is, for the most part, grounded.
Digital does have a drawback, but one that is becoming less of an issue with every successive generation of projector technology. That challenge is a requirement to “project black” onto the dome. An OM projector shines a narrow point of light onto a matte gray surface in a dark room—brilliant stars onto a canvas of “space.” Yet, the digital projector must project both the stars and the darkness of space. If you watched the last season of Game of Thrones, you got a first-hand demonstration of how digital screens can struggle to handle black levels. “Dark isn’t dark,” says Marc Horowitz at the Hubble Planetarium.
Depending on who you talk to, it is acknowledged that full-dome video digital planetariums deliver a somewhat compromised simulation of the night sky, due to resolution and contrast limitations—but those limitations are constantly being overcome and reduced. While stars in the actual night sky appear as quite tiny pinpoints, star size in a digital planetarium is constrained by resolution—a star can be no smaller than a single pixel. The true contrast ratio of a video projector caps out at approximately 10,000:1, producing a bit of a gray level that can be detectable to the dark-adapted eye.
Sky-Skan’s John Stoke says that while 2000:1 black-to-white contrast ratio on a cinema display “looks great,” the same contrast ratio on a planetarium dome “looks like light pollution.” Also, digital projectors have challenges when reproducing the hyper-accurate night skies of the OM projector. Digital projectors must balance brightness and contrast. Stoke says, “You don’t want it to be too bright—it looks like astro-photographs” that populate many of our Instagram feeds these days.
In the night sky, not every star has the same brightness. OM projectors deal with this by limiting the amount of light representing each star. On a digital projector, the default way to make a star appear brighter is by making it larger. This creates accuracy issues with the star field as compared to the true night sky. According to Zeiss, an OM projector can create stars as bright as 1000 lux, while the brightness of a star on a digital system averages 50 lux. Versed in both digital and optical mechanical systems, Mystic Seaport Museum’s Brian Koehler is also the president of the Mid-Atlantic Planetarium Society. “I applaud the manufacturers of digital projection systems for their tireless efforts to increase the quality of their star fields. They recognize the standard that optical-mechanical has set, and digital projectors are getting closer and closer to matching OMs in the authenticity of the night skies that they create,” says Koehler.
Aware of the limitations of digital projection, Zeiss’s hybrid offerings are using “True Black Projection Technology” and has just released the third generation of its VELVET projectors that are specifically designed for planetarium projection. According to Zeiss’s Volkmar Schorcht, the VELVET projectors have a native on-off contrast of 2,500,000:1 to provide “a pure black background and, therefore, perfect edge blending” to allow them to work seamlessly in conjunction with Zeiss OM projectors.
Konica Minolta’s Steve Hatfield says, “The upside to a multiple projector system is a beautiful, high-resolution image, assuming each projector is aligned and blended properly. There are several disadvantages to this kind of system. More projectors means more computers, and more potential points of failure. Projectors and lamps do not age identically, which means that over time, the audience will likely see seams that will appear at some point between each projector's projected image quadrant as the system ages. More projectors, more computers, more lamps, more maintenance etc. means more money. This is true with the up-front cost, as well as future expenditures for operational expenses for lamps, laser diode, or laser phosphor light sources—although not nearly as often as lamps—and occasional individual projector replacement.”
The Henry B. DuPont III Planetarium at the Discovery Museum, in Bridgeport, Connecticut, is currently looking at acquiring a digital system. Planetarium Director David Mestre acknowledges that “digital projection is getting better and better, but an argument can still be made for optical-mechanical projections.” He finds that the OM projector is “a more natural way to teach” audiences about the night sky, but he adds that digital projection allows for more “immersive experiences.”
Planetariums need to make money to stay in business, and the more seats you can fill, the more money each show can make. OM projectors take up space in the center of the theater—an area where seats can be placed. Most digital systems mount the projectors on the periphery of the dome, allowing for maximum seating. With a central projector, the seats that are taken up by the projector’s footprint could add up to a lot of revenue over time.
Another digital advantage that planetariums have discovered is the ability to provide visuals for disciplines of science outside astronomy. Mestre says that “planetaria are exploring other visual science applications in different fields of science that lend themselves to dome projection.” Digital projection allows for different revenue streams than the traditional planetariums do, so much so that Spitz’s Seale notes that the name planetarium is being pushed aside a bit. Some facilities are using the phrase “Learning Dome,” he explains, adding that a group of high school art students recently projected an immersive view of the Sistine Chapel in a dome to study the painting.
Former optical-mechanical projector company, Spitz, is now owned by Evans & Sutherland, and they have delivered more than 500 digital planetarium systems around the world. Spitz Marketing Manager Chris Seale says, “Our users keep surprising us with their cleverness and creativity. And a high-quality digital planetarium with software for immersive teaching of multiple subjects can be had for much less than an optical-mechanical projector. While they may not deliver the same level of night sky simulation fidelity, most planetarium operators find the digital star field totally acceptable in exchange for vastly increased versatility and affordability.”
Obsolescence is another cost factor when deciding between an OM, digital, or hybrid system. According to Steve Hatfield, at Konica Minolta, the average lifespan of an 8K or higher resolution system is seven or eight years, while an OM projector could run for 25 to 30 years. The solution for some is to invest in the OM projector and go hybrid with a lower-resolution digital system that eventually gets replaced. With both systems, annual maintenance is crucial.
E&S’s Niskach thinks that, due to the help of LED technology and other advancements, digital system lifespans are ever-increasing. In April E&S announced DomeX, an LED system of extreme brightness, contrast, and resolution for a black dome system—building a 20-meter demo in China.
With ever-advancing digital technology, is the optical-mechanical planetarium projector going the way of the dinosaur? Not quite. There is zero doubt that the digital planetarium show is the way of the future. Being able to virtually fly through time and space is amazing, but, having seen some of the world’s premier digital systems next to some of the world’s best optical-mechanical projectors, I can honestly say that digital does not own the night sky. Indoors, there is nothing quite as beautiful as the star field projected by a classic (or super-modern) OM projector. E&S’s Scott Niskach says, “No matter how modern a planetarium becomes, it all comes back to telling a great story and getting people engaged with science.”
I would like to thank the following individuals, institutions, and corporations for their time and assistance with this article.
Dave Bush, Director, Charles and Helen Reichert Planetarium, Vanderbilt Museum, Centerport, NY.
Renée Gamba, Director, Museum of Natural History and Planetarium, Roger Williams Park, Providence, RI.
Dr. James Hedberg, Director, City College of New York Planetarium, New York, NY.
Marc Horowitz, Director, Edwin Hubble Planetarium, Edward R. Murrow High School, Brooklyn, NY.
Brian J. Koehler, Supervisor, Treworgy Planetarium, Mystic Seaport Museum, Mystic, CT, and President-Elect of the Middle Atlantic Planetarium Society
David Mestre, Manager of STEM Learning Programs, Director of the Henry B. duPont III Planetarium, Discovery Museum, Bridgeport, CT.
Mike Shanahan, Director, and Mary Meluso, Communications Director, Jennifer Chalsty Planetarium, Liberty Science Center, Jersey City, NJ.
John Stoke, VP for Marketing and Sales, Sky-Skan.
Marc Taylor, Manager, Planetarium and Science Programs, Hudson River Museum Planetarium, Yonkers, NY.
Owen Phairis, Director/Owner, Planetarium Projector Museum, Big Bear Lake, CA.
Jon Elvert, Director of Sales and Marketing, ASH Enterprises, Inc.
Steve Hatfield, Sales Manager/Consultant, Konica Minolta Planetarium Co., Ltd.
Scott A. Niskach, Director of International Sales, Evans & Sutherland Computer Corporation
Chris Seale, Marketing Manager, Spitz, Inc.
Volkmar Schorcht, Carl Zeiss Jena Gmbh, Planetariums
