X-ray crystallography has become the most common way for structural biologists to obtain the three-dimensional structures of proteins and protein complexes. However, crystals of large macromolecular complexes often diffract only weakly (yielding a resolution worse than 4 Å), so new methods that work at such low resolution are needed. Here a new method is described by which to obtain higher-quality electron density maps and more accurate molecular models of weakly diffracting crystals