In electron microscope studies of crystalline solids there is a broad
class of very small objects which are imaged primarily by strain contrast.
Typical examples include: dislocation loops, precipitates, stacking fault
tetrahedra and voids. Such objects are very difficult to identify and
measure because of the sensitivity of their image to a host of variables and
a similarity in their images. A number of attempts have been made to publish
contrast rules to help the microscopist sort out certain subclasses of such
defects. For example, Ashby and Brown (1963) described semi-quantitative
rules to understand small precipitates. Eyre et al. (1979) published a
catalog of images for BCC dislocation loops. Katerbau (1976) described an
analytical expression to help understand contrast from small defects. There
are other publications as well.