Lens centering of aspheres for high-quality optics

The assembly effort of optical systems can be reduced immensely by the use of appropriate manufacturing technologies. For refractive optical systems with a common axis of symmetry, lens centering allows a final system assembly with high accuracy and minimal effort, but is today mostly limited to spherical optical elements only. To overcome the current restrictions, a lens centering process for one-sided aspherical lenses was investigated both in theory and practice. The deviation of the rotational aspheric axis from a reference spindle axis is measured precisely with an electronic autocollimator and an additional distance sensor at the same time. Displacements can be minimized by a combination of lateral and rotational alignment motions, aiming at a coaxiality of both axes. In order to achieve a high performance of the entire optical system, the centered lens housings are machined with a diamond tool at their outer diameter, ground, and top surfaces. The feasibility of the complete process was proved by machining several aspherical lenses and measuring the final assemblies with a coordinate measuring machine. Thereby, a residual decenter <1 µm for the aspheric vertex and a tilt <0.5 arcmin between the aspheric axis and the axis of symmetry of the lens housing could be verified. The achievable manufacturing tolerances prove the practicability of the proposed lens-centering process for a majority of high-quality optical applications.