The Light-Based Technologies Inside Your Favorite Digital Camera

GoPro and smartphone photo apps like Snapchat have these three inventors to thank

10 August 2015

This year marks the IEEE Photonics Society’s 50th anniversary as well as the International Year of Light and Light-Based Technologies. Here, we present some of the members who developed technologies that manipulated light to advance photography and medicine.

Cameras have become part of almost everyone’s culture. They are one of the world’s most popular consumer devices, and the images they produce surround us every day. They all rely on light—not only the external light sources used to enhance images but also the silicon semiconductors in cameras that sense light and produce pictures. Three IEEE Fellows ushered in some of the most transformative developments in photography.

FREEZE-FRAME AND FLASH

If you’ve ever admired a photo that captures stunning details of a moving object seemly frozen in midair, you have IEEE Fellow Harold E. “Doc” Edgerton to thank. He invented the electronic stroboscope, the electronic flash, and slow-motion photography, as well remote-controlled deep-sea cameras.

While a research assistant at MIT in 1931, Edgerton took earlier stroboscopes used in labs and improved on them by developing an electronic version. A stroboscope illuminates a subject for extremely short intervals, allowing a moving object to appear momentarily frozen in place. An amateur photographer, he recognized his invention had photographic potential. A camera could now record an object moving in strobe light as an overlaid set of still images. His strobe light equipment, flashing up to 120 times a second, could freeze objects in motion so that they could be captured in sequence on film in the camera.

Edgerton also experimented with circuits that could fire small flashes thousands of times per second, leading to his invention of the electronic flash for still and ultrahigh-speed cameras. Back then, photographers relied on flash powder, a mixture of magnesium and potassium chlorate that created a controlled incandescent explosion. Edgerton’s strobe light contained a bulb full of an inert gas—initially a mercury gas—connected to a battery. The voltage of the battery would excite the gas molecules into an instant flash of bright light. Edgerton’s flash could be as short as only 10 microseconds, or 1/100,000th of a second, and its duration was easy to adjust. And thanks to the battery, the flash could be used over and over. Later, he replaced the mercury gas with xenon, which made for smaller flash tubes. This basic design lives on in the electronic flashes used today.

Edgerton also built a camera that could shoot the equivalent of 500 frames per second, which led to slow-motion photography of high-speed phenomena. Three of his famous series of shots were of a cat being dropped upside down from a height and twisting in midair to land on its feet, a bullet shot through a light bulb, and the motion of a hovering hummingbird’s wings. Photographs like these were collected in Quicker’n a Wink, a movie documentary in which Edgerton demonstrated how stroboscopic photography could show in slow motion events that occur too fast to be seen by the naked eye. It won an Academy Award in 1941 for best short subject.

This video shows Harold E. "Doc" Edgerton's stop motion experiment, in which he captures a bullet piercing through a playing card.

Edgerton also collaborated with underwater explorer Jacques Cousteau to develop the first underwater time-lapse photography in remote-controlled deep-sea cameras.

DIGITAL MEMORIES

An integrated circuit smaller than a U.S. dime that captures and stores light by turning the light into an electrical charge is the innovation behind electronic digital photography. Invented by IEEE Fellows Willard S. Boyle and George E. Smith in 1969, the charge-coupled device, or CCD, is a photosensitive microchip that is 1,000 times more sensitive than the traditional film then used. The two worked as physicists at AT&T Bell Laboratories, in Murray Hill, N.J.

Each CCD chip is composed of an array of metal-oxide semiconductor capacitors, and each capacitor represents a pixel. The array of pixels collects particles of light, or photons, which are stored as electrical charges within the chip’s structure. Photons hitting the pixels are converted to an electrical signal that can be read by electronics and turned into a digital copy of the light patterns falling on the device.

This digital image sensor eventually made chemical film practically obsolete. CCDs have been used in every digital and video camera plus numerous other devices including bar code readers, scanners, and the Hubble Space Telescope.

For their pioneering invention, the two were corecipients of the 1974 IEEE Morris N. Liebmann Memorial Award and the 2009 Nobel Prize for Physics. In his Nobel acceptance speech, Boyle said the two came up with the idea while brainstorming at a blackboard and immediately “knew we had something special.”

CAMERA ON A CHIP

It was in the 1990s while at NASA’s Jet Propulsion Laboratory, in Pasadena, Calif., working to make miniature high-quality cameras to fit into small spacecraft, that IEEE Fellow Eric R. Fossum developed an alternative to CCD. His active pixel sensor or CMOS-APS technology is now just called a CMOS image sensor. This camera-on-a-chip technology is used today in nearly all cellphone cameras, medical devices, surveillance systems, and video recording devices like the GoPro.

Fossum’s CMOS sensor adapted CCD signal processing to put an amplifier on each pixel of the image sensor so as to yield a higher-quality image. CMOS sensors use multiple transistors to amplify and move the charge provided by incoming photons of light, enabling the pixels to be read individually. This method is more energy efficient than CCDs, and the sensors can be manufactured more easily and at a lower cost, leading to less-expensive but higher-quality digital cameras. CMOS sensors have virtually replaced CCDs in today’s cameras.

Fossum was the recipient of the 2009 IEEE Andrew S. Grove Award for his invention.

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