An aspheric lens or asphere is a lens whose surfaces have a profile that is neither a portion of a sphere nor of a circular cylinder. In photography, a lens assembly that includes an aspheric element is often called an aspherical lens.

The asphere's more complex surface profile can eliminate spherical aberration and reduce other optical aberrations compared to a simple lens. A single aspheric lens can often replace a much more complex multi-lens system. The resulting device is smaller and lighter, and possibly cheaper than the multi-lens design. Small glass or plastic aspheric lenses can be made by molding, which allows cheap mass production. Due to their low cost and good performance, molded aspheres are commonly used in inexpensive consumer cameras, camera phones, and CD players. They are also commonly used for laser diode collimation, and for coupling light into and out of optical fibers.

Larger aspheres can be made by diamond turning, a process in which a computer-controlled lathe directly cuts the desired profile into a piece of glass or another optical material. This is a slow process. A faster and newer technology is deterministic microgrinding, where computer-controlled grinding wheels are used to shape the aspheric profile which is then polished to the final shape. Lenses produced by these techniques are used in telescopes, projection TVs, missile guidance systems, and scientific research instruments.

Another method for producing aspheric lenses is by depositing optical resin onto a spherical lens to form a composite lens of aspherical shape.

Lenses