US Patent 11133151 Transmission electron microscope and method of controlling same

A transmission electron microscope includes an electron beam source emitting an electron beam and an illumination optical system for directing the emitted electron beam at a sample. The illumination optical system has a first condenser lens, a second condenser lens, a third condenser lens, a fourth condenser lens, an objective lens, and a condenser aperture disposed at the position of the second condenser lens. The third condenser lens and the fourth condenser lens cooperate to make the position of the condenser aperture and a sample plane conjugate to each other. The first condenser lens and the second condenser lens cooperate to make the electron beam source and a front focal plane of the objective lens conjugate to each other while the conjugate relationship between the position of the condenser aperture and the sample plane is maintained by the third and fourth condenser lenses.