The study of crystal structures by direct visualization of atom positions with high resolution electron microscopy is being extended to the study of the form of individual crystal defects. Methods for computing the images of crystal defects by use of the assumption of periodic continuation provide a means for the essential verification of image interpretations. High resolution scanning transmission electron microscopes should offer important advantages for this type of work, especially in providing a close correlation between images and diffraction patterns of regions of unit cell dimensions. Also modifications to the usual type of scanning instrument should allow an important degree of versatility for obtaining dark-field images to emphasize particular structural features.
The methods of absorption correction are surveyed focusing our attention on the recent development of the empirical evaluations that utilize the intensity variation in the azimuthal scan or in the equivalent reflections. The possibility of application is also discussed from an experimental point of view.