The present invention relates to a device for phase stepping in phase contrast image acquisition, the device (1) comprising: a mobile grating (10); a guiding element (11); a restoring element (12); and a locking element (13); wherein the guiding element (11) is configured to guide the mobile grating (10) between a first position (2) and a second position (3); wherein the restoring element (12) is configured to apply a force to the mobile grating (10); wherein the force is directed from the first position (2) to the second position (3); and wherein the locking element (13) is configured to releasably lock the mobile grating (10) in the first position (2). In an example, during the motion of the mobile grating (10) back to equilibrium, a decoder (11a) for the position of the mobile grating (10) along the guiding element (11) may trigger at least four measurement frames over a period of at least 2*Pi. The invention provides a device (1) for phase stepping in phase contrast image acquisition which provides a fast image acquisition without a significant delay and which reduces positional inaccuracies and which avoids back-lash.