Diaphragm- to reduce the aperture of (a lens, camera, etc.) by means of a diaphragm.
Electromagnetic spectrum- the entire range of wavelengths or frequencies of electromagnetic radiation extending from gamma rays to the longest radio waves and including visible light.
Parallax-an apparent change in the position of an object resulting from a change in position of the observer.
Pentaprism- a five-sided prism that deviates light from any direction through an angle of 90°, typically used in single-lens reflex cameras between lens and viewfinder to present the image the right way round.
aperture- A usually adjustable opening in an optical instrument, such as a microscope, a camera, or a telescope, that limits the amount of light passing through a lens or onto a mirror.
shutter- Photography . a mechanical device for opening and closing the aperture of a camera lens to expose film or the like.
exposure- the act of presenting a photosensitive surface to rays of light.
depth of field- the range of distances along the axis of an optical instrument, usually a camera lens, through which an object will produce a relatively distinct image.
F-stop- the setting of an adjustable lens aperture, as indicated by an f number.
focal length- the distance from a focal point of a lens or mirror to the corresponding principal plane.