We report our experimental results of phase shifting shadow moiré with a constant butunknown phase step to estimate both the wavefront phases and the phase step. Themethod allows phase retrieval from phase shifting interferograms even though thecalibration data of the phase shifter are unknown. Compared with the traditional shiftingshadow moiré method, the proposed algorithm is insensitive to the height dependent effects,which is the main systematic source of error in phase shift shadow moiré whenreconstructing surfaces from fringe patterns. Experiments show that the proposed methodcan effectively minimize the effects of the phase shifting errors and possesses a superiorperformance to existing typical phase shifting algorithms in the shifting shadow moirétechnique.