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

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In CTEMs, LaB₆ or W (tungsten) electron guns are used. The electron rays emitted from the different positions of the electron source and/or with different defoci may be incoherent. Those incoherent rays form the intensity of diffractogram and thus the resulted image is given by an average of a set of images from different angles of the incidence and defoci. Assuming B(s) and F(Δf) are the normalized intensity of the electron source and defocus distribution, the intensity averaging can be given by,

      ---------------- [3728a]

where,
          s -- The ray directions in the incident electron beam
          Δf -- The defocus
          k -- The reciprocal space vector

J(k, s, Δf) is the intensity distribution of the diffractogram, given by,

      ---------------- [3728b]

where,
          ψ(x) -- The electron wave function in real space