A new way of measuring microscope aberrations

Two-fold astigmatism, three-fold astigmatism and misalignment (coma) can be found from the orientations only of the diffractograms of a set of images with injected beam tilts – typically eight images with tilts of equal magnitude and azimuths 45° apart. The spherical aberration must be determined independently, and the defocus is not measured; however, the measurement required is very much simpler than the measurement of image displacements or induced defocus/astigmatism values, and no calibration of the microscope magnification is needed.