a–c, The pupil function of the microscope is obtained using the iterative phase-retrieval method1 on the PSF of the microscope (see Fig. 1b). The amplitude map of the pupil function is shown in a. The light is compressed and shifted toward the left, which agrees with the analysis in Supplementary Fig. 4. The phase map of the pupil function is first fitted with the first 15 Zernike polynomials and then, as shown in b, with the first four Zernike polynomials removed. The coefficients of the 5–15 Zernike polynomials are shown in c. The Strehl ratio of the phase map shown in b is 0.90, which indicates that our microscope has a performance close to the diffraction limit. Three experiments were repeated independently, with similar results.