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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Figure 1977 shows the misalignment of an objective lens, where the off-axis electron beam enters the objective lens. For a specific lens setting, the object ABC forms an image A'B'C'. The image will be changed to A"B"C" (smaller than A'B'C') with a center (B' or B”) formed by the unchanged beam (BB' or BB”) if the objective lens setting is changed. In this case, the back focal plane of the objective lens is also changed. Furthermore, as shown in Figure 1977 (b) this change induces a rotation of the image because of the helical path of the electrons through the lens. This can happen, for instance, when the objective lens current is changed.

Figure 1977. Misalignment of the objective lens: (a) Sweep of the image, and (b) Combination of sweep and rotation of the image on the viewing screen in the EM.

The image in TEM rotates with the change of magnification because the total magnetic flux strength of the lenses changes. Recently, image rotation-free TEMs have been developed by keeping the total flux strength constant even if the magnification is changed.