Science Facts

How Slow Motion Works? – Camera Science

Slow Motion

By searching Google “best slo-mo scene ever,” you’ll find the Matrix “lobby scene” over and over again. It is a 3-minute 13-second tapestry of 74 normal clips and just 35 slow-motion ones. Slow-motion animates sports, sells iPhones, and is so powerful in movies it can make you forget everything else in the scene. How does it work? To demonstrate the principles of slow motion, a world-class juggler show how a lot of the fundamental ideas.

Though the juggling is filmed with a digital camera, the fundamental principles are the same as film. The 1-second clip is shot and played at about 24 frames a second, 24 pictures that standard speed for movies. When playing both clips back at a rate of 24 frames a second, the 60 pictures take two and a half times longer to play than just 24 pictures. That is slow motion! It comes with some technical hurdles, especially when it comes to lighting.

How slow motion works?

Imagine a door opening and closing to let light in. If you take 24 pictures a second, the shutter will be open for about 1/50th of a second to let in the right amount of light for a nice amount of blur in the motion. Not enough blur and things look disorientingly sharp. 1/50th is just right of a cinematic look. When someone takes 60 pictures a second, everything looks darker. That’s because they need to use a higher shutter speed. There’s less time for light to hit the camera’s sensor (or the film).

To lighten it, you have to crank the light or use more sensitive film (or in a digital camera, use a higher ISO setting). These rules are so important to capture any image. The potential to shape motion was obvious from the beginning of photography.

Early film was often, though not always, fed through the camera manually to control the speed of a picture. Camera operators used this to their cinematic advantage. They often cranked too fast to put more film frames in front of the camera in a shorter period. That would record slower motion. Or they undercranked – crank too slow to make things look faster. Movie projectors could be messed with too.

If you bounce the ball on a tennis racket, the speed of the audio and video have to be the same. Otherwise, it falls out of sync. This idea became increasingly important in the late 1920s when films with sound called “talkies” became the norm. They didn’t work if film recording and playback speeds were all over the place, which they were. In 1927, the Society of Motion Picture Engineers noted that the sound recording device “must be perfectly synchronized with the camera.”

The Jazz Singer, the first talkie, a 1927 movie centered on a blackface performer, was made thanks to Vitaphone. Their technology synced recording speed using a mechanical engine, not a person at a crank. The Motion Picture Engineers followed Vitaphone’s standard and settled on 24 frames a second. The confusion about playback and film speed was over. With a standard established, people were free to experiment.

Slow-motion had already been used in science and sports. Beyond sports, there was some slow-mo dabbling in Hollywood, like the dreamlike hunting party photography in this 1932 musical. In 1938, Fred Astaire and Ginger Rogers danced in slow-mo too. But these slow-motion scenes were rare. French Filmmaker and theorist Jean Epstein played with Slo-mo in the Fall of the House of Usher.

He wrote: “Slow motion brings a new set of possibilities to dramaturgy. Its ability to dismantle feelings, to enhance the drama, surpasses all the other known tragic
modes.”

1930’s French film Zero for Conduct featured a slow-motion scene after a pillow fight, and it’s like a Wes Anderson epilogue. Jean Cocteau’s Orpheus used slow motion to add drama to a dreamy sequence. Akira Kurosawa, whose groundbreaking hit Seven Samurai featured slow-mo, helped influence Hollywood to add slow-mo to action and narrative.

No longer just for sports, musicals, or outsider “artistes,” slow-motion appeared at more than 100 frames a second in the final shooting in 1967’s Bonnie and Clyde. By the ‘80s, it was suitable for everything from blood rushing from an elevator to the end of a glorious race. Slow-motion was an established trope by the 1990s – one with rules, and references, and expectations. Even today, some tech obstacles exist.

The film with iPhone has in regular motion and slow motion. Notice that noise? That’s the phone compensating for less light by making the sensor more sensitive, raising the ISO. But for movies, with speeds at thousands of frames a second possible, and VFX augmentation common. Slow-motion has fully become an aesthetic storytelling tool rather than a technological hurdle. It was obvious from the beginning of photography, but now slow-motion has developed a full range of meanings and uses. It can make 3:13 seconds iconic.


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