star aberration

The star aberration, one of the third-order axial geometrical aberrations, is a parasitic aberration exhibiting two-fold symmetry. (Note that it is called a fourth-order aberration in terms of the wave aberration.) The star aberration cannot usually be detected due to the existence of a large spherical aberration of the objective lens, but is detected after correcting the spherical aberration of the objective lens. The star aberration appears as a pattern with a two-fold symmetry in high angle areas of a Ronchigram. In the case of a TEM equipped with a Cs corrector, prior to microscope observation, aberrations are measured and then the aberrations including the star aberration are corrected by the automatic aberration correction function with the use of the deflectors of the Cs corrector.

Related Term(s)