Harold "Doc" Edgerton » Techniques

Time lapse photography

lisanti — Mon, 19 Oct 2009 19:49:55 +0000

Edgerton took his strobes under water to record the leisurely life of the sea floor, using time-lapse photography.

This method combines a motion-picture camera with a strobe. At regular intervals, the strobe flashes and a single frame of film is exposed and advanced. When the movie is shown at normal speed, the action is speeded up greatly, turning barely-perceptible movement into rush hour.

Watch this video in which Doc Edgerton explains the benefits of “speeding up” and “slowing down” time!

Stroboscopic

lisanti — Mon, 19 Oct 2009 19:49:32 +0000

The strobe light’s ability to create optical illusions enables people to see images that occur too fast for the human eye to discern.

You can see the strobe in action in Doc’s machine he termed the “piddler, ” in which two water streams flow downward and intersect above a catch basin. When a strobe light is used to illuminate the water streams, you can see the water stream as individual “droplets” of water. By adjusting the frequency of the strobe light, you can make the droplets appear to be stationary in midair. In addition, by further changing the frequency of the strobe light, you can make the stream of water droplets appear to flow upwards as well!

Sonar

lisanti — Mon, 19 Oct 2009 19:49:02 +0000

When a strobe would not do the trick in murky waters, Edgerton began working on sonar techniques to “see” with sound. Sonar works by bouncing a sound signal off to something. By measuring the time that it takes for the signal to return, the distance to the object can be calculated.

Doc’s “pinger” measured the distance to the sea bottom. The “boomer’s” signal probed beneath the ocean floor. And the side-scan “fish” was used to find objects that projected up from the bottom. Doc found several sunken ships with side-scan sonar.

Watch this video about sonar “making pictures” with sound!

Shadow Photography

lisanti — Mon, 19 Oct 2009 19:47:43 +0000

Shadow photography is a simple way to stop a fast-moving object. No camera or lenses are used. Instead, the object – for instance, a bullet in flight – passes between the flash and the film. Using wires or a microphone for synchronization, the flash goes off when the bullet is just in front of the film. As it flies by, the bullet casts a shadow on the film and the shadow prevents that part of the film from being exposed. The developed film shows the dark image of the bullet. The earlier photographs of bullets in flight were made this way in the nineteenth century, but Edgerton also used the technique for a range of subjects, from bullets to brine shrimp.

WATCH THIS VIDEO! Lecturer Charles E. Miller creates a shadow photograph.

Schlieren

lisanti — Mon, 19 Oct 2009 19:47:22 +0000

We are surrounded by events that we cannot see. Maybe they happen too quickly for our eyes to catch them or too slowly for us to notice. Or maybe they are normally transparent, like the vortices produced by a rotating fan blade or the heat rising from a candle flame. With mirrors or lenses and a camera, schlieren photography lets us see these things.

In zigzag fashion, a beam of light is reflected form a mirror, past the subject – for instance, a burning candle – to another mirror and then into the camera’s lens. But as the light passes through the hot air above the flames, it is bent, or refracted, slightly. The camera is set up to block out the light that is not refracted and to receive the light that is, giving us an image of the candle and its plume of hot air.

Learn more about how to do schlieren from Professor Vandiver’s site.

View search results for schlieren on this site.

WATCH THIS VIDEO! Professor Kim Vandiver demonstrates the schlieren technique.

Rapatronic Shutter

lisanti — Mon, 19 Oct 2009 19:44:24 +0000

After World War II, the Atomic Energy Commission contracted Edgerton, Germeshausen, and Grier to photograph atomic bombs as they exploded. How to deal with the blinding light, the need to be miles away from the explosion, and the speed of the nuclear reaction in the bomb were problems the trio were asked to solve. The solution was the rapatronic (for Rapid Action Electronic) shutter, a shutter with no moving parts that could be opened and closed by turning a magnetic field on and off. The duration of the exposure was as little as two microseconds.

Multiflash

lisanti — Mon, 19 Oct 2009 19:44:19 +0000

When you take a picture, you usually photograph one image per frame of film. But in a multi-flash photograph, several exposures are made on a single negative. Multi-flash photographs are taken in a darkened room with the camera’s shutter wide open. The film is exposed only when the stroboscope flashes.

The rate of the flash determines the number of pictures on the negative: from a few, separate images (like Doc’s photographs of high-speed divers), to may overlapping ones (like his photographs of golf and tennis swings).

High Speed Camera

lisanti — Mon, 19 Oct 2009 19:40:42 +0000

Edgerton synchronized his electronic stroboscope with a special high-speed motion-picture-camera so that with each flash, exactly one frame of film was exposed. The number of flashes per second determined the number of pictures taken.

Motion pictures are normally exposed and projected at 24 frames per second, but when pictures are made at a higher rate and projected at normal speed, the apparent movement is slowed down. Edgerton designed high-speed motion-picture cameras that could expose as many as six thousand to fifteen thousand frames per second. When these films were projected at normal speed (24 frames per second), very high-speed events appeared – and could be studied – in extremely slow motion.

Nighttime Photography

lisanti — Mon, 19 Oct 2009 02:32:26 +0000

On the eve of World War II, the army asked Edgerton to build a strobe for nighttime aerial reconnaissance photography. The components of the system were bigger and more powerful than anything Doc had previously designed. The aerial camera looked much like a 35mm camera – only it was about two feet long. The flash tube was a monster, made of thirty inches of tough, quartz glass coiled into a spiral. The tube was positioned in a thirty-inch reflector pointing down from the plane’s belly or tail. Banks of capacitors, weighing up to five hundred pounds each, were slung on the plane’s bomb racks.

The flash’s most famous test came on June 5, 1944. Over the D-Day target areas, the airborne photographer opened the camera’s shutter and triggered the flash. The photographs of the quiet nighttime landscape showed that the Normandy invasion was not expected in the designated landing area.