Dioptrialuku

Dioptrialuku is a Finnish term that translates to "diopter number" or "dioptric power" in English. It is a unit of measurement used in optics to quantify the refractive power of a lens or a system of lenses. Specifically, it represents the reciprocal of the focal length of a lens, measured in meters.

The formula for dioptric power (D) is D = 1/f, where 'f' is the focal length in meters. For example, a lens with a focal length of 0.5 meters has a dioptric power of 2 D (1 / 0.5 = 2). A lens with a focal length of -1 meter has a dioptric power of -1 D. Positive dioptric values indicate a converging (convex) lens, while negative values indicate a diverging (concave) lens.

In the context of eyeglasses and contact lenses, the dioptrialuku is used to prescribe lenses that correct refractive errors such as myopia (nearsightedness) and hyperopia (farsightedness). An optometrist or ophthalmologist determines the appropriate dioptrialuku for a patient based on their vision examination. For instance, a prescription might specify a certain dioptrialuku for distance vision and another for near vision, or it might involve different dioptrialukus for each eye. The term is also used in discussions about the optical properties of telescopes, microscopes, and cameras.