An asphere or aspheric lens is an optic whose surfaces are defined by a polynomial equation. Aspheres are rotationally symmetrical around the optical axis, but their radius of curvature changes with the distance from the center. Aspheric lenses provide higher performance compared to conventional lenses, allowing a reduction in size, mass, and number of elements used – important features for miniaturization. Manufacturers of medical instruments, telescopes, and cameras use aspheres to improve their products. As the saying goes, “Where there is light, there must be shadow” and in the case of aspheres, the production and metrology of such lenses requires more complex and innovative technologies compared to traditional lenses.
There are several methods to quantify the surface accuracy of aspheres, both contact and non-contact devices are used by different manufacturers.