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 1973 shows the structure of the electron probe-forming system in STEM mode in JEOL JEM-2010F TEMs. A setup, consisting of electrostatic gun lens and twin condenser lens system, controls the de-magnification of the Schottky field emission source. Compared to the cold field emitter, the Schottky electron source has a much larger emission area. Each element of the electron source can be assumed to emit electrons incoherently and thus results in an incoherent broadening of the probe [1]. A large de-magnification factor between the source and probe reduces this probe-broadening effect. In addition, the beam current decreases due to the probe-forming aperture. A cross-over is formed between the two condenser lenses (C1 and C2) by employing near-maximum excitation in the C1 lens, resulting in a large source de-magnification. The C2 lens and the gun lens are used to tune the probe coherence further by setting the probe size. In the STEM mode, both condenser and objective mini-lenses are tuned off.

[1] J.M. Cowley, Image contrast in transmission scanning electron microscopy, Appl. Phys. Lett. 15 (1969) 58-60.