Specimen throughput in TEM observation is mainly limited by the time involved in switching the electromagnetic lenses. Such lens transitions are required when images are recorded at different magnifications, with different accelerating voltages of the electron beam, or in different imaging modes. The transition consists of the following procedure:
         i) The voltage of the corresponding lens is changed to the new operating condition.
         ii) The magnetic flux density within the lens is led as fast as possible to a steady level very close to the new operating condition.
         iii) The focal settings of the lens are optimized by using image-based feedback techniques.

In practice, control strategies are used to decrease both the maximum transition error (1-5% of the full range) and the maximum transition time (~0.5 s) involved in the switch of the electromagnetic lenses.