Slow-Mo Footage Reveals How Old Film Movie Camera Really Work

The pandemic has limited The Slow Mo Guys’ ability to film grand experiments with their high-speed cameras. But while safely staying home, they’ve found other fascinating things to shoot, including an old 16-millimeter movie camera that when torn apart finally reveals why film is punched full of holes.

If your age means your experience in movie making has been limited to shooting with a smartphone, this look at the inner workings of an old film camera might not be as satisfying as it is to those of us who grew up with grandparents making home movies on loud contraptions that look like they hearken back to the olden days of Hollywood.

Long before digital video was a thing, long strips of film were run through a camera while a series of complex mechanisms exposed single frames 24 times every second. Unlike a modern DSLR camera, which uses a shutter that opens and closes not unlike a garage door, film cameras used a spinning wheel as a shutter, exposing film every time a gap in the wheel passed by. But one question that a lot of people ask about old film cameras is why the images weren’t always blurry as the strips of film appeared to be in constant motion as they ran through the camera?

The simple answer, as revealed in this slo-mo footage captured at 1,000 frames per second on a Phantom Flex 4K camera, is that the film wasn’t constantly moving, it only seemed like it was. Instead, a mechanism that was perfectly synced to the spinning shutter activated a small arm that reaches up, grabs onto one of those holes in the film, and then pulls it down to reveal the next area that hasn’t been exposed yet. This action happens every time the rotating shutter is blocking light, but it then leaves the film stationary for 1/24 of a second during an exposure, so there’s no motion blur.

It seems simple enough, but old film cameras are a remarkable feat of engineering given the speed and accuracy at which they run. The complex mechanisms also explain why the cameras were so loud and required those giant boom mics on set to record the audio of performers without picking up all the extra racket.