In Figure 3162 (a), the spectrum is formed in the dispersion plane, consisting of a distribution of electron counts (I) versus energy loss (ΔE). All the electrons suffering the same energy loss but traveling in both on-axis and off-axis directions are directed to a focus in the dispersion plane of the spectrometer, which acts as a homogenous magnetic lens as shown in the equivalent schematics in Figure 3162 (b). The object plane of the spectrometer is typically set at the back focal plane (crossover) of the projector lens.

Figure 3162. (a) Schematic showing magnetic prism, and (b) Equivalent schematics of the magnetic prism. Electrons at various kinetic energies (due to energy losses induced by interaction with TEM specimen) are focused at the energy-dispersive plane of the spectrometer.