| **Diopter** is a unit of measurement of the refractive power of a lens.
**Definition**
A diopter (D) is a unit of measurement of the refractive power of a lens, defined as the reciprocal of the focal length measured in meters.
**Explanation**
* A higher diopter value indicates a stronger lens, meaning it bends light more strongly.
* A lower diopter value indicates a weaker lens, meaning it bends light less strongly.
* A positive diopter value indicates a converging lens (which focuses light), while a negative diopter value indicates a diverging lens (which spreads light).
**Example**
* A lens with a focal length of 1 meter has a refractive power of 1 diopter (1/1 = 1 D).
* A lens with a focal length of 0.5 meters has a refractive power of 2 diopters (1/0.5 = 2 D).
**Uses**
Diopters are used in
* **Ophthalmology** To measure the refractive error of the eye and prescribe corrective lenses.
* **Photography** To indicate the refractive power of camera lenses.
* **Microscopes** To measure the magnification power of microscope objectives.
**Note**
The term "diopter" is derived from the Greek words "dia" (through) and "optron" (vision).
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