A method for measuring an minimizing the effects of geometric unsharpness in mammography involves using a star resolution pattern to determine the equivalent focal spot size of mammographic X-ray units. With this measurement, the limit of resolution at any plane within the breast of the patient and the focal spot-to-object distance necessary to obtain the desired limit of resolution are determined. Six mammographic X-ray units were evaluated with this technique. The resolution capability of 4 of these units is limited by geometric unsharpness, such that the resolution capability of present mammographic recording systems is not fully utilized.