IMAX 15/70 Film Cameras Are Loud Because They Move Huge Film and Use Vacuum Suction

Traditional IMAX filmmaking is not for novices. The entire process is time-consuming and expensive, and most filmmakers do not make their next movie using 70mm IMAX film. An IMAX 15/70 film camera is bulky and expensive to operate. Even if money is not a problem, the noise remains. When the camera starts rolling, it emits a non-stop mechanical whine. The enormous strip of film racing through it must be held completely flat while each frame is exposed, and the vacuum system that performs that role adds to the noise.

To understand the volume, Engadget goes back to basics. Film cameras record a series of still images. Each frame must be held motionless behind the lens while it is exposed, with the camera advancing the film and repeating the process. A standard cinematic film camera usually completes that cycle 24 times every second. An IMAX camera has much more film to move. The format is known as 15/70 because each frame on a 70mm projection print spans 15 perforations, the small sprocket holes that run along the edges of the film and help the camera position each frame. During filming, the camera runs a 65mm negative horizontally, again using 15 sprocket holes for each frame rather than the five used by a conventional 65mm camera. The resulting image ends up being roughly three times larger.

At 24 frames a second, that means 360 sprocket holes of film a second. That is 5.6 feet per second, or 336 feet a minute. Each 1,000-foot film magazine provides around three minutes of recording time. Moving that much film requires a powerful motor. The movement, along with the camera's magazine and shutter operation, adds more noise. The film has to repeatedly move and settle into place. The sheer size of the film and camera, and the speed at which the film must move, help create a mechanical rattle that is likely audible in behind-the-scenes footage.

The vacuum system is another major source of noise. Each frame needs to sit completely flat behind the lens, but film can easily retain some curl after it has been wound inside a magazine. A small bend that breaks the plane of focus can ruin the entire film. To fix that, IMAX cameras use a vacuum plate behind the lens. It creates suction that pulls the film flat against the plate during exposure. The vacuum is not there to force the film through the camera, but only to help position each frame accurately. To create the vacuum, suction runs as the film moves through the camera. The pump and movement of air create one of the biggest quality-of-life issues with traditional IMAX cameras: a high-pitched mechanical hum that can badly affect recording in the wrong environment. If suction is lost, there is a risk of film bends that affect quality.

The noise is one reason IMAX movies are not the dominant format in movie theaters. Most modern cinematic releases are filmed digitally, and those that are not are probably using cameras that are less bulky and expensive. For instance, 'Filmed for IMAX' movies such as Mission Impossible: The Final Reckoning do not use film at all, but they are still shown in IMAX movie theaters. They use IMAX-certified digital cameras and feature scenes that use the expanded 1.90:1 aspect ratio. Because those cameras are entirely digital, the noise issue is avoided.

Even without a digital IMAX camera, filmmakers have ways to offset noise pollution, although the methods do not remove it completely. IMAX cameras do not lend themselves to small, intimate sets or quiet moments of dialogue, but they are considered perfect for big action scenes with lots of noise. No Time to Die used its IMAX cameras mainly for action and stunt sequences with minimal dialogue. Any dialogue spoiled by the IMAX camera can be rerecorded later using automated dialogue replacement, or ADR, in postproduction. There are also physical ways to offset the issue. A 'barney,' a kind of soft-padded cover, can help reduce some of the mechanical sounds in IMAX setups.