Because of its close relationship with the DPR and the FRC, the method of Young's fringes (Frank et al., 1970; Frank, 1972a, 1976) should be mentioned here, even though this method is nowadays rarely used to measure the resolution of computed image averages. However, Young's fringes shed an interesting light on the relationship between common information and correlation. The method is based on the result of an optical diffraction experiment: two micrographs of the same specimen (e.g., a thin carbon film) are first brought into precise superimposition, and then a small relative translation Ax is applied. The diffraction pattern (figure 3.22) shows the following intensity distribution:
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