Optimal fine ϕ‐slicing for single‐photon‐counting pixel detectors

The data‐collection parameters used in a macromolecular diffraction experiment have a strong impact on data quality. A careful choice of parameters leads to better data and can make the difference between success and failure in phasing attempts, and will also result in a more accurate atomic model. The selection of parameters has to account for the application of the data in various phasing methods or high‐resolution refinement. Furthermore, experimental factors such as crystal characteristics, available experiment time and the properties of the X‐ray source and detector have to be considered. For many years, CCD detectors have been the prevalent type of detectors used in macromolecular crystallography. Recently, hybrid pixel X‐ray detectors that operate in single‐photon‐counting mode have become available. These detectors have fundamentally different characteristics compared with CCD detectors and different data‐collection strategies should be applied. Fine ϕ‐slicing is a strategy that is particularly well suited to hybrid pixel detectors because of the fast readout time and the absence of readout noise. A large number of data sets were systematically collected from crystals of four different proteins in order to investigate the benefit of fine ϕ‐slicing on data quality with a noise‐free detector. The results show that fine ϕ‐slicing can substantially improve scaling statistics and anomalous signal provided that the rotation angle is comparable to half the crystal mosaicity.