International
Tables for Crystallography Volume B Reciprocal space Edited by U. Shmueli © International Union of Crystallography 2006 
International Tables for Crystallography (2006). Vol. B. ch. 2.5, p. 283


Figure 2.5.2.3
The functions , the phase factor for the transfer function of a lens given by equation (2.5.2.33), and for the Scherzer optimum defocus condition, relevant for weak phase objects, for which the minimum value of is . 