Ptychography is an imaging technique, which collects a set of diffraction patterns obtained by illuminating the small regions of an object. When the distribution of light within the region is known, the recovery of the object from ptychographic measurements becomes a special case of the phase retrieval problem. In the other case, also known as blind ptychography, the recovery of both the object and the distribution is necessary. While some iterative approaches for solving blind ptychography are available in the literature, their properties and behavior are scarcely understood. In this talk, we propose a generalization of the Amplitude Flow algorithm for phase retrieval, a gradient descent scheme for the minimization of the amplitude-based squared loss, and show that it has guaranteed sublinear convergence rate.