optics

The word optics refers to the science and technology regarding the behavior and handling of visible light, the term being used for the principles and mechanisms of telescopes and telescopic instruments such as cameras/imagers and spectrographs. It is sometimes analogously used regarding other parts of the electromagnetic spectrum, especially portions of ultraviolet and infrared spectra that are adjacent to visible light, that are handled using virtually the same type of equipment. The adjective optical is also sometimes meant to encompass near infrared and/or near ultraviolet.

A branch of the science that deals with aspects of optics that are unexplainable by regarding EMR as classical waves is termed quantum optics.

The word optics is often used for a telescope or instrument's optical devices or the optical portion or aspect of a device. EMR further from visible light has some parallels regarding design and the word optics is often used, e.g., X-ray optics.