Books that are useful:
- Harburn, Taylor & Welberry, "Atlas of Optical Transforms" -a book of optical transforms illustrating various aspects of diffraction. If you can explain them all, you understand all of diffraction.
- Drenth, J. "Principles of Protein X-ray Crystallography" - a reasonably advanced book directed specifically toward macromolecular crystallography.
- Cantor & Schimmel, "Biophysical Chemistry Part II: Techniques for the study of biological structure and function" - of interest are chapter 13, "Xray crystallograpy' and chapter 14, "Other scattering and diffraction techniques"
Also, an elementary introduction to crystallography can be found in:
- Gale Rhodes, "Crystallography Made Crystal Clear"
- "Graphing Calculator" -(generally available on Macs; I don't know about PCs) useful for graphing scattering functions, etc.