To get that perfect, crystal clear image of a moment frozen in time, three important factors need to work together to produce a high-speed photograph:
Because the actions being recorded take place too quickly for the eye to see, fast-moving and sometimes unpredictable objects need to be detected remotely. This is essentially the subject of the picture letting the camera know when to shoot. By hooking a variety of triggers -- including sound, vibration, contact or light interruption -- electronically to a flash unit, the high-speed object can "tell" the flash almost instantly when to let out a burst of light.
The sound of a gun firing the bullet in this photo actually triggered the flash, not the photographer.
Sound triggers are commonly used in high-speed photography, mainly because they're easy to make and use. There are essentially three parts to a sound trigger: the microphone, the amplifier and a silicon-controlled rectifier (SCR). Instead of using a regular microphone like the kind you see on a theater stage, photographers can use piezoelectric film, a pressure-sensitive film that reacts to sharp sounds like a balloon pop, broken glass or a hand clap. Sound picked up by the piezoelectric film is boosted by the amplifier, which sends an electric current to the SRC. The SRC, connected to the flash unit by a cathode and anode, acts as a switch for the burst of light by shorting the flash. If the object is photographed in a completely dark room, the shutter of the camera can remain open without exposing the film.
If a photographer is shooting outside and relying on fast shutter speed, the timing of the shot is also very important, of course. The camera must be synchronized to shoot a photograph the very moment an object crosses the frame. This involves knowing the delay time between the object's movement and the amount of time your camera requires to take a photograph.
Imaging is simply the process of light painting an image onto the filmstock. Sometimes the type of film a photographer uses can affect the outcome of a high-speed picture. High-speed photography takes into account film speed, or the film's sensitivity to light. Film speed measurements are commonly referred to as an ISO (named so for the International Organization for Standardization), and the lower the ISO, the longer it takes for light to expose on the film. A film with a speed of ISO 800, for example, is faster and more sensitive than one with a speed of ISO 100. Because high-speed photographers use low light levels, they typically use faster speeds in order to make up for the short bursts of light used.
Even with very precise preparation, high-speed photographers rely on luck as much as tight organization to get that great shot. Catching a perfectly shaped drop of water can take more than a hundred shots over several painstaking hours. To some, however, the possibility of stopping time and seeing something no one's ever seen before outweighs the time invested.
For more on the science of photography, see the next page.