 Conversely, the lower the number, the larger the opening, and so the more light that is let into the camera.The wider opening at the lower f-stops narrows the range of focus so the background of an image is blurry when focusing on the foreground, and vice-versa.This "depth of field" increases as the aperture closes, so that objects that are at differing distances from the camera can both be in focus; when the aperture is at its narrowest, the foreground and background are both in sharp focus.