Adaptation of a high-voltage electron microscope for routine biological dark-field imaging

Relative merits of different objective aperture geometries for generating dark-field images in a high-voltage electron microscope (an AEI EM7) are considered. Using metal-bar beam stops in the objective lens diffraction plane, with large (500 micron diameter) limiting apertures, effective resolution in the 2-4 nm range can be demonstrated for biological specimens.