To understand the fundamentals of high-speed photography, it's important to first go over the basics of photography and what makes a camera work. More specifically, it helps to understand how manual cameras work rather than newer automatic and digital cameras. Although it's possible to take photographs of high-speed objects with automatic and digital cameras, when it comes to high-speed photography, the more manual a camera is, the more successful the photos will be. We'll therefore focus on manual single-lens-reflex (SLR) cameras and the basic principles of photography.
One of the most important parts of a camera is, of course, the lens. A lens is a simple, curved piece of glass that bends and redirects incoming light to form a real image, or an exact reproduction of the scene in front of the camera. Light bent through the lens is essentially "painted" onto the film inside the camera; in fact, it's no surprise that the root of the word "photography" is Greek, meaning "drawing with light."
You can't just point a lens at an object and hope your picture will turn out. There are two very important factors that determine how film is exposed to light:
- How much light enters through the lens
- The amount of time the film is exposed to light
The first factor, the amount of light coming onto the film, is controlled by the camera's aperture, which is a circular opening that can expand or shrink in size. The aperture works just like the iris of your eye -- when you need to let in more light, the circle becomes bigger; when you need to block out some light, the circle becomes smaller. A set of numbers on the aperture control of a camera called f-stops describe the size of the circle. The f-stop is inversely related to the size of the aperture: The higher the f-stop number, the smaller the opening. An f-stop of f/11, for example, will be smaller and let in less light than an f-stop of f/8.
The device that works with the aperture and determines the second factor, how long the film is exposed to light, is called the shutter. The shutter is basically a curtain that opens and closes to expose the film to light. More specifically, it's the shutter speed -- the rate at which the shutter opens and closes -- that really affects the film's exposure. Shutter speeds are usually measured in fractions of a second and typically range from one full second to 1/1000th of a second. The longer the shutter remains open, the more light is allowed onto the film.
So how do these factors affect high-speed photography? To learn how high-speed photographers capture such fast action on film, read the next page.