Specimen thickness and image resolution in electron microscopy

The working rule that the resolution obtainable in the electron image of a biological specimen is of the order of one-tenth its thickness is quantitatively explained in terms of the energy loss of electrons scattered in the specimen and of the chromatic aberration of the objective lens. This limitation holds true down to the thinnest sections (100-200 Å) that can be cut at present. That they normally do not show a resolution approaching 20 Å is ascribed to lack of contrast. The use of a filter lens, rejecting all electrons that lose more than 10 V, would improve both contrast and resolution. Its use is even more important for rendering visible carbonaceous structures of size comparable with the instrumental resolving power. A lower accelerating voltage than currently used for electron microscopy is desirable for specimens of poor contrast.