lattice points are close to the Ewald sphere -- they do not have to be exactly on it. Applications Small scattering-angle limit When the wavelength of the radiation to be scattered is much smaller than the spacing between atoms, the Ewald sphere radius becomes large compared to the spatial frequency of atomic planes. This is common, for example, in transmission electron microscopy. In this approximation, diffraction patterns in effect illuminate planar slices through the origin of a crystal's reciprocal lattice. However, it is important to note that while the Ewald sphere may be quite flat, a diffraction pattern taken perfectly aligned down a zone axis (high-symmetry direction) contains precisely zero spots that exactly satisfy the Bragg condition. As one tilts a single crystal with respect to the incident beam, diffraction spots wink on and off as the Ewald sphere cuts through one zero order Laue zone (ZOLZ) after another. See also Bragg's law Laue equations Kikuchi line (solid state physics) References External links Origin of the Ewald Sphere in scattering (TEM) See also Chapter 5 in this web site Diffraction Crystallography