Observations of artefacts in the x-ray ptychography method.

X-ray ptychography, a scanning coherent diffraction imaging method, was used to reconstruct images of a "Siemens star" test pattern with amplitude and phase contrast. While studying how the use of illumination with an increased bandwidth results in clear improvements in the quality of image reconstructions, we found that an artificial change in the overall distance scale factor of the algorithm leads to a systematic response in the image, which is reproduced with an incorrect number of spokes. This pathology is explained by the conflict between the length scales set by the scan and by the diffraction patterns on the detector. (C) 2014 Optical Society of America