In the present paper third order chromatic aberrations have been computed for an immersion lens and an einzel lens based on canonical aberration theory. The electron trajectories with up to third order chromatic aberrations have been compared with the real trajectories. They are in good agreement, and the computational errors are believed to be about 0.2percnt;. Therefore, the canonical theory of higher order chromatic aberration has been verified. As a practical application, for a typical electrostatic lens, the first, third order chromatic aberrations and the third order geometric aberrations, which are functions of the object side beam halfhyphen;angle, have been presented in detail. It is expected that the results are useful for designing and optimizing a low chromatic aberration electrostatic lens.
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