Using impact--factor representation, we consider the lepton pair production by an incident high--energy photon in a strong electromagnetic field of a nucleus. By summing leading terms of perturbation series, we obtain a simple formula for the amplitude, valid to all orders in O(ffZ) and arbitrary field of the nucleus. Using these results, we derive, in a simple manner, the results for the lepton pair production by a virtual incident photon in a Coulomb field. For real incident photon our results coincide with the known ones. Also, a particular example of a non--Coulomb potential is discussed in some detail. 1 Introduction QED processes in the strong Coulomb field attracted considerable attention recently. The understanding of such processes is important for accurate background estimates in heavy ion collisions. Moreover, their analysis is also interesting from pure theoretical point of view. Indeed, the accuracy of perturbative calculations in this case is determined by a parameter..
