A method and apparatus for performing an X-ray diffraction measurement with a diffractometer having an X-ray beam directed at a sample and a two-dimensional X-ray detector includes the performance of a physical scan during which the detector is moved through a scanning range in an angular direction about the sample position. To provide a uniform exposure time, the detector, when located at an extreme of the scanning range, is controlled to progressively change the portion of the detected X-ray energy that is used at a rate that maintains a uniform exposure time for each angular position in the scanning range. Alternatively, when located at an extreme of the range, the detector is kept stationary until a desired minimum exposure time is obtained for each angular position, after which the collected diffraction data is normalized relative to exposure time.