We demonstrate that the non-steady-state photoelectromotive force induced by a vibrating Ronchi grating has a very complicated but deterministic dependence on the propagation distance. The characteristic minima of this dependence are found at fractional values of the Talbot distance, and their width is determined by the maximal transversal spatial frequency resolved by the system. This permits high accuracy in the determination of the Talbot distance. © 2013 Optical Society of America