dioptre
Sign in to savethumb|Illustration of the relationship between optical power in dioptres and focal length in metres. A dioptre (British spelling) or ' (American spelling), symbol dpt or D', is a unit of measurement with dimension of reciprocal length, equivalent to one reciprocal metre, . It is normally used to express the optical power of a lens or curved mirror, which is a physical quantity equal to the reciprocal of the focal length, expressed in metres. For example, a 3-dioptre lens brings parallel rays of light to focus at metre. A flat window has an optical power of zero dioptres, as it does not cause l
AI overview
A dioptre is a unit of measurement used to express the optical power of lenses and curved mirrors, defined as the reciprocal of the focal length measured in metres. It matters because it provides a simple way to describe how strongly a lens or mirror focuses or spreads light—for example, a 3-dioptre lens brings parallel light rays into sharp focus at one-third of a metre away.
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Key facts
- Unit.name
- dioptre
- Unit.quantity
- optical power
- Unit.symbol
- dpt
- Unit.symbol2
- D
- Unit.units1
- SI units
- Unit.inunits1
- 1 m−1
via Wikipedia infobox
Article
6 sectionsContents
- Name, symbol
- In vision correction
- Curvature
- Relation to magnifying power
- See also
- References
thumb|Illustration of the relationship between optical power in dioptres and focal length in metres. A dioptre (British spelling) or ' (American spelling), symbol dpt or D', is a unit of measurement with dimension of reciprocal length, equivalent to one reciprocal metre, . It is normally used to express the optical power of a lens or curved mirror, which is a physical quantity equal to the reciprocal of the focal length, expressed in metres. For example, a 3-dioptre lens brings parallel rays of light to focus at metre. A flat window has an optical power of zero dioptres, as it does not cause light to converge or diverge. Dioptres are also sometimes used for other reciprocals of distance, particularly radii of curvature and the vergence of optical beams.
The main benefit of using optical power rather than focal length is that the thin lens formula has the object distance, image distance, and focal length all as reciprocals. Additionally, when relatively thin lenses are placed close together, their powers approximately add. Thus, a thin 2.0-dioptre lens placed close to a thin 0.5-dioptre lens yields almost the same focal length as a single 2.5-dioptre lens.