Illustration of the ptychographic XST method. The beamline illumination was focused (off-axis) in two dimensions by two linear focusing lenses, with numerical apertures of 0.015 (horizontal) and 0.014 (vertical). The Siemens star sample was placed 371 µm downstream of the focal plane. Images were recorded on a CCD pixel array detector 0.71 m downstream of the focus. The scan data consist of 49 shadow images, recorded as the sample was translated across the beam profile. The wavefront phase and reference maps were refined iteratively.