The review and comparison of the operation of aberration corrected instruments in the CTEM and STEM configurations is discussed. Electron optical correctors provide significant control over many other aberrations and introduce certain higher-order aberrations along with correction of the spherical aberration. The image aberration is defined as the differential of the wave aberration function, which is calculated as the distance between the aberrated and ideal wave surfaces in the diffraction plane. The influence of lens aberrations in CTEM image formation can be described by multiplying the electron wave in reciprocal space. Aberration measurement methods for STEM also include to tilt the illuminating beam through the corrector while using a relatively small beam-limiting aperture such that different illumination angles are explored.