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Ultra High-Speed Cameras: Filming the Impossible

Written by Laura Davies

https://pxhere.com/en/photo/995445

High-speed photography has gifted us with a lot of incredible videos. With it, we’ve recorded the motions of a hummingbird’s wings, various fruit exploding, and the graceful ripples of cheek and lips as a man gets punched in the face. What would the Matrix have been without slow-mo and how much better is the world for the glorious 7 minutes of Alan Rickman making a cup of tea?

https://libreshot.com/the-train-enters-the-tunnel-at-high-speed/

All fascinating and enlightening, but ultimately things most would think easily possible with modern technology. But ultra-high-speed cameras have gone further. With frame rates of over 1 million per second we can now film the impossible. We’ve recorded photons travelling at the speed of light and have watched the ripples they make when they collide with an object, like a stone in a pond. The highest spec cameras can see around corners. We can even extract the audio of people’s voices from silent film by analysing the vibrations of a nearby box of tissues. None of this should be possible, but here we are, in the future and everything.

 

From Newspapers to Peepshows

So how did we get here? High-speed cameras date back further than you might think, beginning with William Henry Fox Talbot in 1851 and a standard wet plate camera. He wanted to capture an image of a section of the London Times newspaper as it was spun on a wheel. The wet plates he was using consisted of glass coated with albumen, silver nitrate, and water and had a very low sensitivity to light. If he exposed them to the spinning newspaper at ambient light for long enough to form an image, the wheel would’ve spun so many times that the result would’ve been a blurred streak. To get around this, he set everything up in a darkened room and used a Leyden jar to emit a flash of light only 1/2000th of a second long. This was bright enough to form the image and quick enough that the section of newspaper hadn’t spun away. The developed photos were so successful that the text was completely legible. He’s not often given credit for his contributions to High-speed photography, as his work wasn’t followed up for another 20 years, but he was the first to prove it was possible to capture motions previously too fast for the human eye to see.

The next great leap in the journey to Ultra-High-speed cameras was made to settle an argument. In 1872, Californian Governor Leland Stanford was having a disagreement about whether or not horses lift all four feet off the ground as they gallop. He commissioned photographer Eadweard Muybridge to settle the matter and presumably prove him right. Muybridge tried taking ordinary stills of a horse at first but couldn’t get a decent shot. As you can’t have a horse ride through a pitch dark room without risking serious injury, Talbot’s spark in the dark technique was also out. He needed to use a shutter, but the ones available just weren’t fast enough.

https://commons.wikimedia.org/wiki/File:Animal_Locomotion._An_Electro-Photographic_Investigation_of_Consecutive_Phases_of_Animal_Movements._Commenced_1872_-_Completed_1885._Volume_IX,_Horses_MET_DP275235.jpg

His efforts were interrupted when he was put on trial for the murder of his wife’s lover. He was acquitted on the grounds of justifiable homicide as the jury all agreed they’d have done the same thing if another man had impregnated their wife. So, Muybridge avoided prison but his photography work was delayed. Finally, in 1878, using twenty-four separate cameras and a thread controlled shutter release system of his own invention, he captured the series of images that settled the argument once and for all. Yes, horses do lift all four feet off the ground as they gallop.

After putting that to rest, he continued his work in developing better cameras with the capacity to capture more rapid movements. He switched from thread to clockwork and managed to reduce his shutter exposure times to 1/1000th of a second. This was still only half Talbot’s speed but the payoff was he didn’t require complete darkness. His most notable achievements were developing a technique for photographing the beating of a dog’s heart and the invention of the Zoopraxiscope, a device used to show his photographs, in sequence as a moving image. This was probably the first time motion photography was ever applied to physiological research. It was also the inspiration for Kinetoscopes, the early peephole motion picture devices, and Mutoscopes, the racy peepshow machines. As, with many scientific breakthroughs, someone saw and admired the feat of engineering and responded with, “Yes, it’s marvellous, but how can we use it for porn?”

https://commons.wikimedia.org/wiki/File:Muybridge%27s_zoopraxiscope_and_disc.jpg

 

The Father of High-Speed Photography

In the years that followed, a number of photographers and engineers continued the work, and roll film was invented, which was a vast improvement over plates, and shutter speeds increased. However, one stumbling block remained. Light. As you reduce the shutter speeds, you need to increase your light levels to ensure enough reaches the film to form your picture. This vital step was taken by Harold Edgerton, the so-called father of the high-speed camera and once named by National Geographic “the man who made time stand still”. I’m sure both William Talbot and Eadweard Muybridge would dispute this, but since when was history ever fair and maybe if Muybridge hadn’t wasted all that time killing a guy things would be different.

Edgerton’s breakthrough came in the late 1920s during his time as a student at MIT. He was working with a rudimentary computer and noticed that the blinking warning lights seemed to cause some moving parts of its motor to freeze. This gave him the idea that split-second bursts of light could revolutionise the world of high-speed photography. If this breakthrough sounds incredibly similar to Talbot’s 1851 spark technique, you’re not wrong, and photographers had been using a rudimentary flash for years. The problem was, that it involved the use of flash powder, a mixture of magnesium and potassium chlorate, and what was essentially a small, controlled explosion. It could only be fired once so was no use in generating a series of images. It was also difficult to ignite at a precise time and the duration was hard to control.

Frustrated by this, Edgerton decided to create a means of lighting his pictures himself and invented the flashbulb. A glass bulb filled with a gas that would create a bright light once connected to a battery. Its duration could be controlled and reduced to 1/100,000th of a second, and it could be lit again and again. He called it the stroboscope, and with it, captured some of the most iconic images in history. A seemingly solid golf ball deforming when hit; a boot sinking into a football as it was kicked; and the crown of milk forming around a single droplet on impact. These were things no one had realised were happening in front of their eyes every day and the physics involved in the liquid droplet is still not fully understood.

https://picryl.com/media/skc7108-918814

Although his photos were beautiful, he wasn’t an artist and said so on many occasions, famously stating, “Don’t make me out to be an artist. I am an engineer. I am after the facts, only the facts.” His picture of a bullet flying through an apple was pretty, but pretty pictures weren’t the purpose of his flashbulb. He knew it had greater potential.

https://flic.kr/p/2hMpr58

Initially, he approached Kodak with his invention, but they didn’t think there was a market for it. In response to the slight, he took his camera to a boxing match and captured the knockout blow. This would’ve been next to impossible with flash powder due to the difficulty in controlling the timing of ignition. Edgerton took his pictures of the exact moment glove met jaw and wired them to every newspaper in the country. Kodak got interested.

Later, he created a giant version of the stroboscope and pitched it to British intelligence chiefs for use in reconnaissance. They said it had no practical purpose in war so, true to form, Edgerton flew 10,000 ft. over Stonehenge on a moonless night and sent them the photos. Of course, they soon adopted it and used it to identify landing sites for allied paratroopers in Normandy.  Before he came along, they’d been dropping bombs loaded with 500 lbs of flash powder and timing them to explode in mid-air. This had limited photos to two per plane. The strobe light could bring home multiple images and was capable of illuminating targets from 4 miles away.

Unfortunately, some people are hard to impress, and he met a huge amount of resistance when he arrived at Chalgrove airbase to train the pilots. They wanted to fight, not take pictures, and purposefully performed poorly during training in the hope of being transferred. Edgerton’s response was to send pilots on training missions to Britain’s largest nudist colony. Pretty soon the underperforming pilots were returning home with some of the sharpest images yet.

Throughout the war Edgerton made numerous contributions, photographing rifle shots to prove recoil didn’t affect accuracy, helping to develop armour-piercing shells by inventing a sound-triggered strobe to record the moment of impact and modifying his strobe lights into landing beacons that are still used today.

 

Faster than a Nuclear Bomb?

The contribution of high-speed photography to the war effort and vice versa didn’t end with lighting. Scientists working on the Manhattan Project were having problems with energy levels in the first stage of the explosions. No one could get to the source of the issue until a technician, Berlyn Brixner, suggested photographing the explosion with high-speed cameras and they started developing their own.

Manhattan Project Scientist W. Gregory Marley was the first to step up to the plate with the Marley camera. It worked by spinning a wheel of little slots in front of an array of cameras. It’s speed was incredibly helpful in the development stages and he brought it with him to Los Alamos. Unfortunately, it was already obsolete before the 1945 Trinity test as head of the Optics in Weapons Physics division, Professor Julian Ellis Mack developed his own camera that put Marley’s to shame. His Mack streak camera was a rotating mirror camera able to capture images at 1/10 millionths of a second intervals. Finally, a camera worthy of the title of Ultra-High-Speed.

In the end, scientists decided not to put all their eggs in one basket as atomic bombs are pretty expensive and had 52 cameras trained on the explosion. In total, 100,000 images were taken of the Trinity test and the photos are terrifying and mesmerising in equal parts. Beyond this, they were also vital in working out issues in detonation timings and calculating the time taken to reach critical mass.

After the Manhattan project ended and not to be outdone, “If you don’t wake up at 3:00 AM to start testing your ideas, then you are wasting time.” Edgerton was back on the scene for the hydrogen bomb tests at Eniwetok Atoll in 1952. He knew he could improve on the speeds of the rotating mirror cameras and developed the Rapatronic (Rapid Action Electronic) Camera. It used 2 polarizing filters as a shutter which would change polarity when hit with an electronic pulse and allow the light through. This meant there were no moving parts to slow things down and it achieved shutter intervals of an astonishing 1/10 billionth of a second.

https://commons.wikimedia.org/wiki/File:RapatronicCameraAWTM.jpg

The Fastest Camera to Date

While it would’ve been nice to leave the achievement of the fastest ever camera with someone as iconic as Edgerton, technology has advanced and high-speed photography has only become faster. One of the most significant changes was, of course, the move from film to digital. This opened up the massive potential for increasing framerates as engineers were no longer hampered by pesky film.

The first impact of this was the opportunity for continuous recording or cyclical buffering. When working with film, a photographer has a tiny window in between beginning a recording and their film running out. Not such a problem if they were smashing something with a bat or dropping a watermelon off a roof, but anything involving an uncooperative subject was a challenge. Plus, at more than a million frames per second, the amount of film required was getting ridiculous. With digital recordings, a computer can continually overwrite the data until the event has occurred and the photographer hits stop.

Of course, this advancement is really just a matter of convenience. The race for faster frame rates is where the true challenge lay. So what do you think we’ve reached today? 100 billion, maybe a trillion per second?

Thanks to the work of Professor Lihong Wang, we can now capture a mind-boggling 70 trillion frames per second. Making it a form of ultra-high-speed photography that deserves it’s own name, Femto-photography. Wang uses a technique called CUSP, or compressed ultrafast spectral photography. It relies on short pulses of laser light, each lasting one quadrillionth of a second or, one femtosecond.

Remarkably, for something so quick, the process takes place in two stages, imaging and illumination. In the imaging phase, an interchangeable lens system captures the scene with an external camera and a digital micromirror device that encodes the image into a binary pattern and relays it to a streak camera. In the illumination phase, a beam splitter breaks a laser pulse into small oscillations that occur 70 trillion times per second. Each pulse triggers a sensor in the camera which then captures an image.

Why Do We Need Femto-Photography?

Why would we ever need cameras to work this fast? High-speed cameras are incredibly useful in crash tests, sports analysis, and identifying weaknesses in manufacturing processes. Ultra-High Speed cameras are no good for the majority of these applications. Working at 70 trillion frames per second the cameras have to produce images with incredibly low resolutions or you’d simply run out of space to store them. Plus, you’d have to work with events of really short durations. No possibility of watching a slow-mo. belly flop or even capturing a whole sneeze.

Fortunately though, the technology isn’t going to waste. Scientists began by filming the speed of light by firing packets of photons and watching as they fly through a coke bottle and scatter on impact with the lid. While it’s incredible to literally watch the speed of light it’s also a huge step forward in observing the behaviour of protons. 

The observations have led scientists to be able to use the cameras to film things that are not in front of the lens. They can do this by firing a laser, bouncing it off a wall and round a corner and recording the photons that come back. This might sound incredibly impractical when you could just put a camera on a stick and pop in round the corner. But, imagine the technology installed in a self-driving car. Blind bends would no longer be blind as the car could be continuously firing lasers to build a picture of things a standard camera couldn’t see. It could also be miniaturised and used in medical technology, in cameras needed to probe round folds and bends in our bodies. It even opens up possibilities for watching the signals travelling through our neurons and deepening our understanding of the human brain.

Another, admittedly less wholesome, application is the possibility to generate audio from a silent video recording. Every sound we make produces vibrations, and these are transferred, invisibly to the naked eye, to objects around us. If you discuss classified information near a houseplant, its leaves will move almost imperceptibly to the sound of your voice. With an ultra-high-speed camera, these movements, no larger than 1,1000th of a pixel, can be recorded from across the street through a soundproof window and converted back into speech. They’ve even managed to identify whether the speaker is male or female through the vibrations of a box of tissues.

If you think you could avoid spilling national secrets by listening to your intelligence through headphones, you’d be wrong. These cameras can generate speech or music through the vibrations of a headphone cord. And this isn’t theoretical, it’s already been done with some very creepy recordings of Mary Had a Little Lamb, why is it always children’s nursery rhymes?

What else could today’s Ultra-High-Speed cameras be used for? It’s really up to the imaginations of scientists and engineers across all fields to figure out how the technology could be applied to their own work. Fortunately, the Femto-photography team have open-sourced all of their data in the hope someone will do just that, and make more impossible things possible.

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