Speed and sensitivity of new pixel array detectors bring new possibilities to the measurement of X-ray diffraction data. Due to their point spread function and their ability to measure weak reflections, reliable estimation of exposition parameters by human eye is made more difficult. However, a correct exposure helps increase the information gain of the measurement (more precise measurement of anomalous differences or weak reflections for improvement of electron density maps) and at the same time reduce radiation damage.
As a signal to noise ratio of individual reflections (I/s) has, with a chosen error model , an upper limit (ISa), the optimal exposure can be estimated from the relation of I/s of strong reflections to ISa. The relation can be analyzed e.g. in a graph of I/s to intensity , which is informative even for initial data containing few frames. Therefore, a script for fast analysis was developed. The script produces graph for optimal exposure estimation before the final data collection.
A preliminary analysis of earlier measured datasets shows that majority of datasets measured with a PILATUS detector is underexposed. In comparison, datasets measured with a CCD detector (marCCD) show correct exposure or overexposure.
This study was supported by BIOCEV CZ.1.05/1.1.00/02.0109 from the ERDF and institutional support of IBT CAS, v.vi.. RVO: 86652036 and by Ministry of Education, Youth and Sports of the Czech Republic (grant No. LG14009) and Czech Science Foundation, project 15-05228S and project 15-15181S.