How Does It Work?

Like early cameras, modern cameras control the amount of light that reaches the film.

The aperture is the opening behind the lens. Its size can be set to let in more light (to capture a dimly lit subject) or less light (for a brightly lit subject). Aperture settings are expressed in f -stops. The higher the f-stop, the smaller the aperture.

The shutter is located between the aperture and the film. It opens and shuts very quickly. This allows the focused rays of light from the lens to strike the film. The speed of the shutter is expressed in fractions from 1/1000th of a second (allows less light) to 1 second (allows more light).

Film comes in different speeds. It is usually rated on the ISO (International Standards Organization) number scale. The higher the ISO rating, the faster the film reacts to light. That is, less light is needed to make a good exposure.

When the photographer presses the shutter release button, the aperture is uncovered and light strikes the film.