> Does f000 mean the direct beam? Having a hard time imagining such a miller
index or the corresponding planes... No, F000 is NOT the direct beam. I may not have made that clear enough in some of my drawings and captions, and it will be emphasized in the second printing/ebook. There is in fact scattering/diffraction in forward (2theta zero) direction, which coincides with, but is entirely different from, the primary beam. Elastically scattered photons experience a 180 degree phase shift, unscattered direct beam photons just experience - nothing. F000 has a clear relation in amplitude and phase (0) to the remaining observable Fs. Not intuitive, agreed. BR PS: Just in case it might come up - there is NO destructive interference between F000 and direct beam - the required coherence that leads to extinction/summation of 'partial waves' is limited to a single photon. Standard (non-FEL) X-ray sources are (with minor exceptions in special situations) not coherent. Has been discussed many times on bb.
