Attempts to improve the resolution capability of an x-ray imaging system have to include the presence of the patient, particularly the effect of subject motion. From this it follows that the loading capability of the x-ray machine should be an integral part of the analysis and optimization of systems resolution. We have tried to quantify both resolution and load capacity and to merge them in a "figure of merit," which seems helpful in judging focal spot performance. A true falling load characteristic for the focal spot distribution as well as for the exposure load characteristic appears to give optimum performance in terms of systems resolution. With computer help, we have calculated the pertinent parameters, such as intensity, modulation transfer, load, and temperature, as functions of spatial and temporal coordinates.