Magazine article American Cinematographer

Some Facts about Omnimax

Magazine article American Cinematographer

Some Facts about Omnimax

Article excerpt

The OMNIMAX projection system installed in San Diego's Reuben H. Fleet Space Theater has many similarities to our IMAX system which is being used in the Cinesphere in Toronto- but there are also several very important dissimilarities.

Let's start with the similarities. The OMNIMAX projector's mechanical mechanism incorporates the same rolling loop, 70mm, 15-perforation-per-frame film transport as the IMAX projector. The reel system is somewhat the same: two feed reels and two takeup reels. This arrangement enables the film to be simultaneously run and rewound, so that programs won't require too long of an interval between starts.

OMNIMAX has essentially the same auxiliary equipment as the IMAX system. It has a rectifier. It has a coolant conditioning unit to provide distilled water to cool the lamp and other components in the lamphouse. It has an electrical control cabinet and an air compressor to supply air for the rolling loop mechanism itself.

The dissimilarities between the two systems lie mainly in the arrangement of the equipment, the lamphouse and the lens. The 12-kilowatt xenon lamphouse on the OMNIMAX projector is completely new and was designed and built by Optical Radiation Corporation in Azusa, California. The lamphouse had originally presented a problem, because we didn't have the room to put in a big, tall lamphouse such as the one we have in Toronto. The OMNIMAX lamphouse is currently being run with 10-kilowatt lamps in it and these lamps are considerably smaller than the ones that are in the projector in Toronto. We are using 20-kilowatt lamps there now and have used lamps as high as 25 kilowatts. The lamps we are using in San Diego are a bit less expensive and they should have a somewhat longer life. We are expecting a lamp-life of around 750 hours. In Toronto we are getting about 600 hours with the 20,000-watt lamps, and we've run many lamps with a 400-hour life.

The shape of this lamphouse is much different from that of the previous one. It has optics that are designed for projection purposes, whereas the other one was based on a solar simulator lamphouse and had a quite different beam characteristic.

Perhaps the most radical difference between the two systems is the unique "two-part" design of the OMNIMAX projector. In a dome theater it is necessary to locate the projector somewhere near the center of the auditorium, but if you provide a full projection booth at that point, you lose too many seats in the theater. As a result, the OMNIMAX projector has been mounted on an elevator which travels fourteen feet on rails up into a tubular "doghouse" which is actually in the theater and the lens looks out through a port with a motorized door. You cannot use a port glass, as with a conventional projector, because you are projecting with a 180° wide-angle lens, which must actually be in the theater.

The doghouse enclosure into which the camera moves is such a tight fit that there isn't room even for anybody to crawl up on either side of it. The projector can't be loaded or unloaded or maintained while it is in operating position, so it has to come back down into the lower level of the theater in order to be loaded and set up. The reels of film have been left down below, because the request was for a 45-minute film. In the large IMAX format 44 minutes (the actual length of our show) adds up to some 15,000 feet of 70mm film on a 45-inch reel and the combined weight of film and reel is approximately 200 pounds.

As the projector head moves up into its enclosure, the reels remain below and the film chases up and down over rollers to run through the projector and get back down again to the reels. After the screening, the projector moves back down into the projection room for loading and unloading and whatever maintenance is required. That elevator capability involves us in a whole system of remote controls. There is a control console and an operator's platform so that the operator can get at things when the projector comes back down. …

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