Design and experimental validation of novel enhanced-performance autofocusing microscope

Autofocusing is a critical operation in automated microscopy applications in the automated vision inspection, measurement and manufacturing fields. The present group recently developed a novel optics-based autofocusing microscope incorporating two achromatic lenses, which provided a large linear autofocusing range, a rapid response, and a high focusing accuracy (Liu et al. in Appl Phys B 109: 259-268, 2012). In the present study, the focusing accuracy of the microscope is further improved by replacing the two achromatic lenses with two cylindrical lens assemblies. The autofocusing performance of the modified microscope is characterized numerically by means of ZEMAX simulations and is then verified experimentally using a laboratory-built prototype. The experimental results confirm that compared with the original microscope with achromatic lenses, the modified microscope achieves a greater focusing accuracy (focusing accuracy of <= 1 mu m, repeatability of +/- 1 mu m).