Aberration correctors have become essential equipment for high-resolution imaging and spectroscopy in STEM and CTEM. This is impressively documented by the large and still rapidly growing number of hexapole-type imaging and probe correctors installed all over the world. The optical design of the hexapole Cs-correctors in essence is based on the theoretical studies of Rose [1, 2] . It has been put into practice by Haider et al. during 1992Haider et al. during -1997 and consists of a hexapole

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... let and two transferlens systems. This design provided the basis for the CEOS imaging correctors (CETCOR) which are available for a variety of commercial TEM instruments. Subsequently, a similar design could be used to correct for the spherical aberration of the probe-forming system in a STEM, as well. Nowadays, it is not uncommon to have a double-corrected instrument with a probe corrector above and an imaging corrector below the objective lens. 934