High-Speed Cameras: The Key Technology Behind "Time Warp"

Flippin’ Through the Motions

If you've ever played with a flipbook or drawn one yourself, you've seen firsthand how your brain can interpret still images as movement. The image on each page is a little different from the one before, and as you flip through them, your mind blends them into movement. Just like turning a novel's pages moves you through a story, turning the pages of a flipbook moves you through an action.

This same concept is behind photographs that freeze phenomenally brief moments in time, like the instant a bullet passes through a playing card. It's also at the heart of videos that slow down rapid motion, like the bursting of a soap bubble, so you can see what happens one split second at a time.

In a flipbook, the action is usually a little jerky -- each picture is different enough from the next that your eyes and brain can detect the difference. But the more pictures you add to the stack, the smaller those differences are until eventually the motion looks completely smooth. With enough subtly different images, you'll reach a point where the flipbook includes details that pass by too quickly for you to perceive them. You can only see them if you pull out a single page or flip the pages slowly.

The Briefest of Flashes

In still photography, you can capture such brief moments with an ordinary camera, as long as you're taking the picture in a completely dark room. The camera's shutter, which normally opens just long enough to let light hit a piece of film or a digital sensor, stays open in the dark. At just the right moment, the flash illuminates the scene for a fraction of a second. Because it's the only instant that there's light in the room while the shutter is open, it's the only moment the camera records. Usually, a switch controls this process, detecting sound, vibrations or pressure from the moving object and instructing the flash to fire.

High-speed video requires more than an ordinary video camera -- but it got its start with still cameras. In the late 1800s, photographer Eadweard Muybridge used multiple still cameras to record the movements of animals. Among his discoveries was the fact that there are moments when all four of a horse's hooves are off the ground when it gallops. The trick to Muybridge's research was using enough cameras to divide the movement into small enough parts to analyze.

Recording at Top Speed
In a digital high-speed video camera, a sensor records the light. The sensor is typically a charge coupled device (CCD) or a complimentary metal oxide semiconductor (CMOS) sensor. You can read about how each of these sensors records light in How Digital Cameras Work. The sensor reacts to changing light and sends signals to the camera's storage -- either dynamic random access (DRAM) or flash memory. The sensor, its processor and all the controlling circuitry all have to be fast enough to record the light from thousands of images every second.

What Can You See? 
Playback of these recordings provides more than just astounding visuals of the world in slow motion. It's how high-speed imaging expert Matt Kearney from Tech Imaging and the rest of the crew create slow-motion footage for Discovery’s slow-motion science show, "Time Warp." Researchers can also use high-speed cameras to study everything from the way a dog drinks to the movement of a hummingbird's wings. In manufacturing settings, a high-speed camera can pinpoint exactly what's going wrong on an assembly line that's causing the process to break down. High-speed cameras have even been used to evaluate different methods of stringing tennis rackets and document the way lightning branches when it strikes. The two largest users of high-speed video are the automotive crash testing industry and those involved in military and ballistics testing. NASA has also been known to use its share of high-speed imagery technology.