Is a hole or an opening, mechanically controlled or not, that allows light to be passed through a lens and onto an image plane. Aperture is often referred in photography as a dial or a command wheel setting which in turn controls a mechanical or electronic device that opens up, or closes down the diameter of the opening. Thus increasing or decreasing the amount of light passed through the lens. F-stop, Step up, step down, and F, are also terms that are used to describe adjustment of the Aperture.