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A capital D, optical power as a reciprocal metre.
Also known as: Diopter, Optical power, Lens power, Refractive power
A dioptre is one reciprocal metre given a different name for optical work, and its value is why spectacle prescriptions add up: put two lenses together and their dioptres sum, where their focal lengths do not.
Denotes optical power, the reciprocal of focal length, expressed in reciprocal metres and named the dioptre.
Contexts: Laboratory
Adds across lenses in contact, which is why prescriptions are written in dioptres rather than focal lengths.
Contexts: Laboratory
Is a special name for the reciprocal metre and is accepted for use with the SI rather than being an SI unit itself.
Contexts: Laboratory
A capital letter D, a vertical stroke with a bowed curve joining its top and bottom on the right.