An aperture is the opening of a camera that can be adjusted to control the amount of light entering the camera. Aligned with the centre of the lens, the aperture is used in conjunction with the shutter to control the time of exposure and to regulate the amount of light entering the camera. The ratio of the diameter of the aperture to the focal length of a lens is expressed as an F-number. A smaller F-number has a larger aperture, meaning that more light travels through the lens to the film.