Analysis of defocus error on the absolute measurement of spherical surface

The spherical absolute measurement is based on the Fizeau interferometry system. The Fizeau interferometer has a common optical path which helps reduce the impact of system-specific errors and has relatively low requirements for environmental changes. In this study, the cat's eye position, confocal position, and confocal rotation 180-degree position involved in three absolute position measurement methods are simulated by using Zemax optical simulation software. The influence of the defocus error on measurement results is analyzed by adjusting parameters. The results of simulation and analysis show that the defocus error will affect the accuracy of the absolute spherical measurement, and the defocus amount and aperture angle will also affect the defocus error.