One embodiment relates to a dual Wien-filter monochromator. A first Wien filter focuses an electron beam in a first plane while leaving the electron beam to be parallel in a second plane. A slit opening allows electrons of the electron beam having an energy within an energy range to pass through while blocking electrons of the electron beam having an energy outside the energy range. A second Wien filter focuses the electron beam to become parallel in the first plane while leaving the electron beam to be parallel in the second plane. Other embodiments, aspects and features are also disclosed.