asfäärinen

Asfäärinen is a Finnish term meaning not spherical, used primarily in geometry and optics to describe shapes or surfaces that deviate from a perfect sphere. The concept covers a wide range of forms, from simple ellipsoids and paraboloids to more irregular and complex surfaces.

In mathematical terms, a sphere is a surface with constant positive Gaussian curvature. An asfäärinen surface does not share that uniform curvature; its curvature varies across points on the surface. This broad category includes many familiar shapes such as ellipsoids, hyperboloids, and paraboloids, as well as more irregular geometries that cannot be described by a single radius.

In practical contexts, asfäärinen surfaces are central in optics and engineering. Aspherical lenses and mirror surfaces reduce optical aberrations and allow more compact, efficient designs than traditional spherical elements. These surfaces are often represented using conic sections (elliptical, hyperbolic) or higher-order polynomial terms to capture the desired shape. Manufacturing techniques include precision grinding and polishing, computer-controlled diamond turning, and other advanced fabrication methods. Metrology and testing focus on accurately reproducing the intended aspherical profile to ensure correct imaging performance.

Common applications include telescopes and cameras, where aspherical optics improve image quality, and eyeglasses, where aspherical lenses can provide better peripheral vision and reduced distortion. The term also appears in general discussions of geometry to contrast non-spherical shapes with the idealized sphere.

See also considerations of asphericity in different disciplines for related concepts and specific use cases.