A diopter is a unit of measurement used to express the optical power of a lens. It is defined as the reciprocal of the lens's focal length in meters-for example, a lens with a focal length of 0.5 meters has a power of 2 diopters (1 ÷ 0.5 = 2).
Diopters are commonly used in photography, optometry, and magnification tools to indicate how strongly a lens converges or diverges light. In practical terms, lenses with higher diopter values provide greater magnification or focusing ability over shorter distances, making them useful in close-up, macro, or corrective optics.