A limiting factor, except in the special case of field-ion microscopy and the atom-probe FIM has been resolution. And while resolution on a fine scale is attainable in the field emission microscope, the form of the specimen as well as the conditions involved in its imaging are not applicable to materials as they exist in the technological environment; nor are the responses noted always unambiguously interpretable on the basis of bulk solid properties of engineering significance. The technological and engineering importance of electron and ion optics, and ion and electron microscopy in particular, are manifest primarily in the ability of these approaches to detect impending structural failure at its inception, and to provide a mechanistic basis for the description of fracture processes. The image formation occurs as a result of electron transmission. It must also be realized that the primary signal information for the formation of the image occurs in the objective-lens section of the electron microscope.