This book (Practical Electron Microscopy and Database) is a reference for TEM and SEM students, operators, engineers, technicians, managers, and researchers.
 

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Under axial illumination conditions it is not possible to measure all aberration coefficients. In this case, only the defocus and the twofold astigmatism can be determined by the defocus-based techniques. The other aberration coefficients, e.g. spherical aberration, need to be provided by the microscope manufacturer or to be determined by different methods. However, those aberration coefficients, such as the axial coma and the threefold astigmatism, cannot be ignored at high spatial resolutions approaching 0.1 nm. Therefore, the measurements of the other aberration coefficients should be done by other methods such as tilting the illumination. Note that we need to realize that tilting illumination also changes the defocus, astigmatism, and the original aberrations.

Although the computational correction of the phase error caused by coma requires the determination of only a small number of parameters, it is harder to determine the values of these parameters from imaging single particles than from imaging 2-D (two-dimensional) crystals [1].

[1] Henderson, R., Baldwin, J.M., Downing, K.H., Lepault, J., Zemlin, F., 1986. Structure of purple membrane from halobacterium-halobium – recording, measurement and evaluation of electron-micrographs at 3.5 Å resolution. Ultramicroscopy 19, 147–178.