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 TV's, 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.
