Cameras are the defining tools of photography, the science which the art could not exist without. Descended from the ancient camera obscura, all cameras share three basic traits: an aperture to focus light, an imaging media (usually film) to record the focused image, and a body to keep unfocused light away from the media. Cameras exist in an variety of forms, ranging from "single-use" disposable cameras to professional SLRs and large format view cameras, while supporting media formats ranging from 19th-century glass plates to 21st-century digital media. The Open Directory organizes its listings of camera resources primarily by imaging media -- the type of film (or non-film) used by the cameras discussed.