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In optics, a pencil or pencil of rays is a geometric construct used to describe a beam or portion of a beam of electromagnetic radiation or charged particles, typically in the form of a narrow cone or cylinder. Antennas which strongly bundle in azimuth and elevation are often described as "pencil-beam" antennas. For example a phased array antenna can send out a beam that is extremely thin. Such antennas are used for tracking radar. See Beamforming for further details. In optics, the focusing action of a lens is often described in terms of pencils of rays. In addition to conical and cylindrical pencils, optics deals with astigmatic pencils as well.〔 〕 In electron optics, scanning electron microscopes use narrow pencil beams to achieve a deep depth of field.〔 〕 Ionizing radiation used in radiation therapy, whether photons or charged particles, such as proton therapy and electron therapy machines, is sometimes delivered through the use of pencil beam scanning.〔 〕 ==See also== *Pencil (mathematics), a family of geometric objects having a common property such as passage through a given point. *Fan beam *Pencil beam scanning (Medical physics) *Microwave transmission 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Pencil (optics)」の詳細全文を読む スポンサード リンク
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