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.