The author presents the results of studying numerical differentiation step influence in photogrammetric equalization tasks on the main characteristics of the resulting solution. A list of the main evaluated characteristics is presented and explanations of their role in the analysis of the photogrammetric equalization results are given. Using the example of several real routes of optical-electronic space survey, experimental calculations were performed, the purpose of which is to establish the dependence of the inverse photogrammetric serif’s main solution characteristics at the stage of numerical differentiation. The results of the equation calculations are analyzed and a conclusion is made on the instability of the estimated characteristics and not quite satisfactory outcome of equalization when assigning a step of numerical differentiation through known methods. A criterion for the optimality of the numerical differentiation step in photogrammetric equation tasks is proposed and an algorithm for calculating the step based on a new standard is developed. Its essence is explained and the graphical interpretation is given. Based on experimental calculations, the effectiveness of the developed criterion is confirmed.