High-speed Photography: Flash Duration, Shutter Speeds and Exposure
To understand high-speed photography, we must also look at its opposite: long or extended exposure photography. This technique involves exposing the film in a camera for longer periods of time -- anywhere from an eighth of a second to several minutes.
Busy traffic scenes in cities during dusk, dawn and nighttime are the types of photos you'll usually see in an extended exposure photograph -- ones in whichthe headlights of cars aren't dots of light but rather long streaks of light that cross the picture, blending into each other. This occurs because the light from a car's headlight actually paints across the frame of the picture and is exposed onto the film for a longer duration.
If you were to take a picture of something like a bullet using the same method of long exposure, you'd barely see a thin streak across the frame of the picture. Because the image of a bullet would cross the camera lens within a fraction of a second, too much light would capture the bullet's entire path from one side of the picture to the other.
The success of high-speed photography largely depends upon how quickly the film is exposed to light. Therefore, high-speed photographers rely heavily on flash units to take pictures, using extremely short flash durations -- the shorter the burst of light, the better. Because of this, many high-speed objects are photographed in complete darkness. In this case, the camera's shutter is simply left open while the shot takes place; if there's no light in the room, the film won't expose. Once the object passes through the frame, the flash unit lets out a burst of light, and that moment is the only thing that gets painted onto the film. Sufficient flash durations can be as short as 30 microseconds, or 0.00003 seconds.
Photographers shooting nature scenes or sporting events that take place outside obviously can't keep everything in complete darkness. In this case, photographers rely on extremely fast shutter speeds. While regular photography taken in sunlight might work with shutter speeds that are 1/125th of a second, shutter speeds for high-speed photography are much faster -- as fast as 1/8000th of a second.
How does a photographer get all of these factors to line up perfectly and result in such clear shots? To learn about detection, synchronization and other important aspects of high-speed photography, read the next page.