Aspheric lens
From Wikipedia, the free encyclopedia
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.
Aspheric lenses are also sometimes used for eyeglasses. These provide clearer vision and a wider unaberrated field of view than conventional eyeglass lenses, and also distort the viewer's eyes less as seen by other people, producing better aesthetic appearance. The complex front surface curves from the center of the lens to the edge. With a prescription for the farsighted, the lens curve flattens toward the edge of the glass, and in the nearsighted, the surface becomes steeper to the lens edge, which offers vision superior to a conventional lens.[1]
[edit] Manufacture
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.
[edit] History
Francis Smethwick ground the first high-quality aspheric lenses and presented them to the Royal Society on February 27, 1667/8.[2] A telescope containing four aspheric elements was judged superior to a "common, yet very good" telescope used for comparison, and aspherical reading and burning glasses also outdid their spherical equivalents.
[edit] References
- ^ Choosing spectacles. Retirement Expert. Retrieved on 2006-10-23.
- ^ (1668) "An Account of the Invention of Grinding Optick and Burning-Glasses, of a Figure Not-Spherical, Produced before the Royal Society" (PDF). Philisophical Transactions of the Royal Society 3: 631. Retrieved on 2006-11-03.
