Pencil (optics): Difference between revisions
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{{Short description|Narrow beam of electromagnetic radiation or charged particles}} |
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[[File:Pencil beam 2.png|right|thumb|A pencil-beam radar]] |
[[File:Pencil beam 2.png|right|thumb|A pencil-beam radar]] |
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[[File:3d-radarp.jpg|right|thumb|A pencil-beam radar]] |
[[File:3d-radarp.jpg|right|thumb|A pencil-beam radar]] |
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In [[optics]], a '''pencil''' or '''pencil of rays''' is a geometric construct used to describe a [[Light beam|beam]] or portion of a beam of [[electromagnetic radiation]] or charged [[subatomic particle|particle]]s, typically in the form of a '''narrow beam''' ([[Cone (geometry)|conical]] or [[Cylinder (geometry)|cylindrical]]). |
In [[optics]], a '''pencil''' or '''pencil of rays''' is a geometric construct used to describe a [[Light beam|beam]] or portion of a beam of [[electromagnetic radiation]] or charged [[subatomic particle|particle]]s, typically in the form of a '''narrow beam''' ([[Cone (geometry)|conical]] or [[Cylinder (geometry)|cylindrical]]). |
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| ⚫ | A 1675 work describes a pencil as "a double cone of rays, joined together at the base."<ref>{{cite web |last1=Bailey |first1=Nathan |title=An Universal Etymological English Dictionary |url=https://commons.wikimedia.org/wiki/File:Pencil_1675.png |access-date=24 November 2022 |date=1675}}</ref> In his 1829 ''A System of Optics'', [[Henry Coddington]] defines a pencil as being "a parcel of light proceeding from some one point", whose form is "generally understood to be that of a right cone" and which "becomes cylindrical when the origin is very remote".<ref>{{cite book |last1=Coddington |first1=Henry |title=A System of Optics: A treatise on the reflexion and refraction of light. -pt.2 A treatise on the eye and on optical instruments |date=1829 |publisher=J. Smith |url=https:// |
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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, and the process is known as [[beamforming]]. |
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, and the process is known as [[beamforming]]. |
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In [[electron optics]], [[scanning electron microscopes]] use narrow pencil beams to achieve a deep [[depth of field]].<ref> |
In [[electron optics]], [[scanning electron microscopes]] use narrow pencil beams to achieve a deep [[depth of field]].<ref>{{cite journal |
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{{cite journal |
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| journal = New Scientist |
| journal = New Scientist |
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| title = The art of seeing the very small |
| title = The art of seeing the very small |
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| date = 19 May 1983 |
| date = 19 May 1983 |
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| url = https://books.google.com/books?id=z0Z3DxacC9IC&q=electrons+%22pencil-beam%22+sem&pg=PA472 |
| url = https://books.google.com/books?id=z0Z3DxacC9IC&q=electrons+%22pencil-beam%22+sem&pg=PA472 |
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}}{{Dead link|date=September 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> |
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}}</ref> |
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[[Ionizing radiation]] used in [[radiation therapy]], whether [[photon]]s or [[charged particle]]s, such as [[proton therapy]] and [[electron therapy]] machines, is sometimes delivered through the use of pencil beam scanning.<ref> |
[[Ionizing radiation]] used in [[radiation therapy]], whether [[photon]]s or [[charged particle]]s, such as [[proton therapy]] and [[electron therapy]] machines, is sometimes delivered through the use of pencil beam scanning.<ref> |
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In [[backscatter X-ray]] imaging a pencil beam of x-ray radiation is used to scan over an object to create an intensity image of the Compton-scattered radiation. |
In [[backscatter X-ray]] imaging a pencil beam of x-ray radiation is used to scan over an object to create an intensity image of the Compton-scattered radiation. |
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==History== |
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[[File:Pencil 1675.png|right|thumb|In 1675, a pencil was interpreted as a double cone of rays, as from an object point, through a lens, to an image point.]] |
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[[File:Ray pencil beam Coddington 1829.png|right|thumb|Definitions of ''ray'', ''pencil'', and ''beam'' in Henry Coddington's 1829 ''A System of Optics'', Part 1]] |
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| ⚫ | A 1675 work describes a pencil as "a double cone of rays, joined together at the base."<ref>{{cite web |last1=Bailey |first1=Nathan |title=An Universal Etymological English Dictionary |url=https://commons.wikimedia.org/wiki/File:Pencil_1675.png |access-date=24 November 2022 |date=1675}}</ref> In his 1829 ''A System of Optics'', [[Henry Coddington]] defines a pencil as being "a parcel of light proceeding from some one point", whose form is "generally understood to be that of a right cone" and which "becomes cylindrical when the origin is very remote".<ref>{{cite book |last1=Coddington |first1=Henry |title=A System of Optics: A treatise on the reflexion and refraction of light. -pt.2 A treatise on the eye and on optical instruments |date=1829 |publisher=J. Smith |url=https://books.google.com/books?id=c8zaAAAAMAAJ |access-date=24 November 2022 |language=en}}</ref> |
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==See also== |
==See also== |
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Latest revision as of 04:22, 19 September 2024
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 beam (conical or cylindrical).
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, and the process is known as beamforming.
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.[1]
In electron optics, scanning electron microscopes use narrow pencil beams to achieve a deep depth of field.[2]
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.[3]
In backscatter X-ray imaging a pencil beam of x-ray radiation is used to scan over an object to create an intensity image of the Compton-scattered radiation.
History
[edit]
A 1675 work describes a pencil as "a double cone of rays, joined together at the base."[4] In his 1829 A System of Optics, Henry Coddington defines a pencil as being "a parcel of light proceeding from some one point", whose form is "generally understood to be that of a right cone" and which "becomes cylindrical when the origin is very remote".[5]
See also
[edit]- Collimated beam
- 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
References
[edit]- ^ Edward L. Nichols & William S. Franklin (1903). The Elements of Physics: A College Text-book. Macmillan Co. p. 77.
- ^ Nick Johnson (19 May 1983). "The art of seeing the very small". New Scientist. 98 (1358): 472.[permanent dead link]
- ^ Faiz M. Khan (2009). The Physics of Radiation Therapy (4th ed.). Lippincott Williams & Wilkins. pp. 521–522. ISBN 978-0-7817-8856-4.
- ^ Bailey, Nathan (1675). "An Universal Etymological English Dictionary". Retrieved 24 November 2022.
- ^ Coddington, Henry (1829). A System of Optics: A treatise on the reflexion and refraction of light. -pt.2 A treatise on the eye and on optical instruments. J. Smith. Retrieved 24 November 2022.
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