- dioptre
[dioptre 词源字典]
- "A unit of refractive power, which is equal to the reciprocal of the focal length (in metres) of a given lens", Late 16th century (originally as diopter, denoting an alidade): from French, from Latin dioptra, from Greek, from di- 'through' + optos 'visible'. The term was used in the early 17th century to denote an ancient form of theodolite; the current sense dates from the late 19th century.[dioptre etymology, dioptre origin, 英语词源]