This book (Practical Electron Microscopy and Database) is a reference for TEM and SEM students, operators, engineers, technicians, managers, and researchers.
 

=================================================================================

Based on the optical reciprocity theorem [1], BF-STEM images can be related to the HRTEM images of an atom as a phase object. Like HRTEM images, BF-STEM images are very sensitive to the focal conditions, and contrast reversal is often observed because of multiple scattering and phase shift due to defocus condition of the lens. A full interpretation of BF-STEM images can be done with phase contrast simulation in the same way as the HRTEM images. [2]

 
 
[1] Born M, Wolf E. Principles of optics. Cambridge, UK: Cambridge University Press; 1997. 
[2] Spence JCH. High resolution electron microscopy. 3rd ed. Oxford: Clarendon Press; 2003.