IMAX (for Image Maximum) is a film format created by IMAX Corporation that has the capacity to display images of far greater size and resolution than conventional film display systems. A standard IMAX screen is 22 m wide and 16 m high (72.6 x 52.8 ft), but can be larger. Currently, IMAX is the most widely-used system for large-format, special-venue film presentations. As of 2006, there were 280 IMAX theatres in 40 countries (60 percent of these are located in the U.S. and Canada). A variation of IMAX, IMAX Dome (originally called OMNIMAX), is designed for projection on tilted dome screens. Films can also be projected in 3D with IMAX 3D. In the late 1960s the San Diego Hall of Science (now known as the Reuben H. Fleet Science Center) began searching North America for a large-format film system to project on the dome of their planned 76-foot tilted-dome planetarium. One of the front-running formats was a double-frame 35 mm system, until they saw IMAX. The IMAX projector was unsuitable for use inside a dome because it had a 12-foot-tall lamphouse on top. However, IMAX Corporation were quick to cooperate and were willing to redesign their system. IMAX designed an elevator to lift the projector to the center of the dome from the projection booth below. Spectra Physics designed a suitable lamphouse that took smaller lamps (about 18 inches long) and placed the bulb behind the lens instead of above the projector. Leitz of Canada developed a fisheye lens that would project the image onto a dome instead of a flat screen. The new system, that the San Diego Hall of Science called OMNIMAX, uses a fisheye lens on the camera that squeezes a highly distorted 180 degree field of view onto the 70 mm IMAX film. The lens is aligned below the center of the frame and most of the bottom half of the circular field falls beyond the edge of the film. The part of the field that would fall below the edge of the dome is masked-off. When filming, the camera is aimed upward at an angle that matches the tilt of the dome. When projected through a matching fisheye lens onto a dome the original panoramic view is recreated. OMNIMAX wraps 180 degrees horizontally, 100 degrees above the horizon and 22 degrees below the horizon for a viewer at the center of the dome. It premiered in 1973 at the Reuben H. Fleet Space Theater and Science Center in San Diego's Balboa Park showing two OMNIMAX features, Voyage to the Outer Planets (produced by Graphic Films) and Garden Isle (by Roger Tilton Films) on a double bill. IMAX has since renamed the system IMAX Dome. Even though the Reuben H. Fleet Science Center – which coined the original name – now uses the new name, many theaters such as the Cincinnati Museum Center still call it OMNIMAX. OMNIMAX theaters are now in place at a number of major American museums, particularly those with a scientific focus, where the technical aspects of the system may be highlighted as part of the theme interest. The projection room is often windowed to allow public viewing and accompanied by informational placards like any exhibit. Inside the theatre, the screen may be a permanent fixture, such as at the St. Louis Science Center (which also plays a short educational video about the OMNIMAX system just before the feature film); or lowered and raised as needed, such as at the Science Museum of Minnesota (where it shares an auditorium with a standard IMAX screen). Before the feature begins, the screen is backlit to show the speakers and girders behind the screen. IMAX Dome screens may also be found at several major theme parks and Las Vegas hotels. But despite their impressive capabilities and unique experience, the system seems likely to remain a novelty rather than a widespread commercial phenomenon. Relative to their size, OMNIMAX theaters are very expensive to build and maintain, and have a relatively small seating capacity. To make matters worse, only those seats closest to the center of the theater provide the full effect of the immersive view. Museums are able to run the theaters at a profit only because they are able to subrogate the construction expenses through grants and public fundraising and then show relatively inexpensive documentary films, often while still being able to keep admission prices lower than those of standard cinemas. In this way, OMNIMAX theaters have become a "cash cow" for financially strapped public institutions.