Adam Savage Reveals the Inner Scale of IMAX 70mm Film Projection

Adam Savage walks into IMAX headquarters in Los Angeles, hoping to get up close and personal with the raw film that creates those immersive visuals on-screen. First, he enters the vault, which houses hundreds of 70mm prints, a bizarre sight. Then he meets with the technicians in the print assembly room, followed by a tour of the projection booth, which serves as the final inspection before the directors give their approval.

The film itself passes through the projector in a format known as 15 perforation. Each frame is ten times the size of a conventional 35mm frame, and there is no capacity for a soundtrack; everything is handled digitally. Adam points out that because the audio strip is not printed on the film, the sound must originate from a separate digital source running alongside it, and it is this extra real estate that gives the IMAX screens their legendary sharpness, allowing them to reach heights of up to 90 feet.

Down in the assembly room, the technicians are working with reels that are taller than most people and weigh significantly more when fully loaded. Adam watches as they disassemble and reassemble reels received from the printing lab. Irving, one of the experienced technicians, has been on the job for thirty-three years and is a bit of a dinosaur. He’s like a huge puzzle master, lining up scenes from all over the place with printed lists to determine where each frame should fit.

The splicing process is done in two stages: first, they make a temporary cut that allows you to easily pull the film apart for inspection, and then they produce a more permanent weld that will withstand the entire run. Adam looks around at the gigantic rewind benches that fill the room and is shocked that even a short segment can weigh dozens of pounds. It all boils down to the thick stock and the amount of visual information packed into each frame.

Loading a finished reel into the projector necessitates a clever pulley system to lift the hefty weight from the ground floor to the booth on the level above. First, the crew threads over a hundred feet of leader film, which provides approximately 20 seconds of run time at the projector’s constant 337 feet per minute speed. That sliver of film guides the true print into place without interfering with the opening frames of the film. To make matters even more complicated for 3D showings, the entire process is practically doubled: you have two identical projectors running left-eye and right-eye prints simultaneously, each fed through its own pulley channel.

Inside the booth, three projector setups sit on a sliding rail system. One manages film, while the other two oversee digital backups, which essentially brighten things up and keep the stereo sound in check. The rail system allows the technicians to quickly slide the units in and out when switching formats. Adam follows the thread path as the film loops from the supply reel, through the projector gate’s super precise sprocket holes, across the lamp house, and back down to the take-up reel along the same route, with each movement perfectly in sync with the separate digital audio track from the hard drive or optical disc.
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