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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The structural difference of round and multipole lenses lead to different lens properties even though both are based on solenoid coils. The most important difference of their properties is that the magnetic field lines in the multipole lenses are mostly perpendicular to the optical axis while the magnetic field lines in the round lenses are greatly parallel to the optical axis. Therefore, based on Lorentz Force theory, the primary force effect of the magnetic field in the multipole lenses can achieve the expected deflection of the electron rays, while the large axial component of the magnetic field in round lenses has only the effect of inducing the electrons trajectories to rotate. That means to achieve the same 'useful' lens functions, multipole lenses only needs much smaller fields (~ one order of magnitude smaller) than round lenses. In this case, the electrical current flowing in the solenoid coils is smaller and produce less heat. The other benefit is that the Lorentz Force in multipole lenses does not rotate the EM images.