High Precision Sphere Correction Using MRF Technology

Case Study Summary

This case study demonstrates the use of Magnetorheological Finishing (MRF) to correct both large convex and deep concave spherical optics to ultra-high precision. Using QED Technologies’ Q-forge platform in rotational mode, sphere correction was performed on 150 mm diameter optics manufactured from soft optical glasses including N-LAF2 and S-FSL5Y.

For the convex optic, a 150 mm polishing wheel and C10+ MR fluid were selected to enable rapid correction of low-spatial-frequency errors while maintaining surface quality. Surface error was reduced from approximately λ/8 PV to λ/27 PV in under 10 minutes, achieving RMS values near 3 nm. For the deep concave optic, a 20 mm wheel and D11 fluid were used to maximize removal rate and ensure mechanical clearance, reducing surface error from λ/10 PV to better than λ/23 PV.

These results highlight MRF’s ability to deliver fast, deterministic correction of spherical optics across a wide range of geometries. The combination of adaptable spot sizes, optimized MR fluids, and precise rotational control enables manufacturers to achieve sub-λ/20 performance with predictable cycle times.