Brechungsfähigkeit

Brechungsfähigkeit, also known as refractive power or dioptric power, is a measure of how strongly a lens or other optical system converges or diverges light. It is the inverse of the focal length, typically measured in diopters (D). A lens with a shorter focal length has a higher refractive power. For example, a lens with a focal length of 0.5 meters has a refractive power of 1 / 0.5 = 2 diopters.

Positive refractive power indicates a converging lens, such as a convex lens, which brings parallel light rays to a focus. Negative refractive power indicates a diverging lens, like a concave lens, which spreads parallel light rays apart as if they originated from a focal point behind the lens. The refractive power of a lens is determined by its curvature and the refractive index of the material it is made from. A higher refractive index or a greater curvature results in a higher refractive power.

In optometry and ophthalmology, refractive power is crucial for correcting vision defects. Prescriptions for eyeglasses and contact lenses specify the refractive power needed to focus light correctly onto the retina. For instance, myopia (nearsightedness) is corrected with diverging lenses (negative refractive power), while hyperopia (farsightedness) is corrected with converging lenses (positive refractive power). The eye itself possesses refractive power, primarily due to the cornea and the crystalline lens, which work together to focus light.