Deep focus is a photographic and cinematographic technique using a large depth of field. Depth of field is the front-to-back range of focus in an image — that is, how much of it appears sharp and clear. In deep focus the foreground, middle-ground and background are all in focus. Deep focus is normally achieved by choosing a small aperture. The aperture of a camera determines how much light enters through the lens, so achieving deep focus requires a bright scene or long exposure. Wide angle lenses also make a larger portion of the image appear sharp. It is also possible to achieve the illusion of deep focus with optical tricks (split focus diopter) or by compositing two pictures together. It is the aperture of a camera lens that determines the depth of field.