Aspheric lens
An aspheric lens is a lens whose surface isn’t part of a sphere. This unusual shape helps light focus more accurately, reducing common optical errors called aberrations. Because of this, a single aspheric element can replace several standard lenses, making cameras, telescopes, and other optical devices smaller, lighter, and sometimes cheaper.
Where they’re used: Aspheric lenses appear in many areas. In cameras (often labeled ASPH), they help create sharp pictures with fewer distortions. They’re common in smartphone cameras and some CD players. They’re also used in eyeglasses to give crisper vision, especially away from the center of the lens, and to make lenses thinner and less noticeable. Aspheres are helpful when the two eyes need different powers (anisometropia). They’re used in wide-angle and fast normal lenses to reduce aberrations, and in catadioptric systems like Schmidt cameras and Schmidt–Cassegrain telescopes. Small aspheres are used to collimated laser beams and to couple light into optical fibers.
Design in simple terms: An aspheric surface can take many shapes, but the goal is to bend light differently from a simple sphere or cylinder. This special curvature reduces distortion and other flaws in the image. Small, inexpensive aspheres are often made by molding; larger, higher-quality ones are ground and polished. Other methods include diamond turning (computer-controlled cutting with a diamond tip), applying resin to a spherical lens to form an aspheric layer, or using masks and polishing techniques to shape the surface precisely. Finishing steps improve smoothness and accuracy.
How they’re measured: Precision matters for aspheres, so engineers test their shapes with optical instruments. Interferometers compare the actual surface to the desired shape to map deviations. For mass production, reference patterns and computer methods help check many lenses quickly and ensure consistent quality.
Eyeglass specifics: Aspheric lenses can be convex (outer surface bulges outward) or concave (inner surface curves inward). Convex aspheres are common for farsighted people and for lenses with progressive reading areas. They can reduce thickness and improve appearance while still providing the needed power. Strong concave aspheres help with severe nearsightedness. In many plus lenses, the outer (front) surface carries the aspheric shape; in many minus lenses, the back surface does.
A short history: The idea of reducing spherical errors with non-spherical surfaces goes back to Ibn Sahl in the 10th century. Early work by Descartes and Huygens explored the concept. Moritz von Rohr is often credited with early eyeglass aspheres, and Francis Smethwick helped advance high-quality aspheric lenses. The first mass-produced aspheric element appeared in 1956 for a 16 mm camera lens.
In brief, aspheric lenses deliver sharper images with fewer distortions, allowing smaller, lighter, and sometimes cheaper optical systems.
This page was last edited on 3 February 2026, at 08:39 (CET).