The Ewald construction: Ewald's sphere of radius (solid circle) depicts all possible scattering wavevectors under the current setup. Lattice planes with Miller indices
(hkl) are represented by points on the reciprocal lattice (black dots). For wavelength λ, no reciprocal-lattice point is on Ewald's sphere implying that no scattering signal will be generated at any scattering angle. If the wavelength is appropriately tuned, some reciprocal-lattice points can fall on the new Ewald sphere (dashed circle) to satisfy Bragg's law, for instance, .