A reference glossary of core photography terms covering exposure, optics, composition, sensor technology, and file formats. Exposure Aperture — The opening inside a lens through which light passes, expressed as an f-number (f/1.8, f/8, f/16). A lower f-number means a wider opening and more light; a higher f-number means a narrower opening and less light. Aperture also controls depth of field: wide apertures produce shallow focus, narrow apertures produce deeper focus across the frame.