A brief overview of the radiological imaging problem is presented, emphasizing the need for parametrizing components for the user, medical physicist, or system designer. Against this background a method is proposed for reducing MTF data. The single parameter obtained is analogous to criteria of “sharpness” used in other optical applications. The example of x‐ray tube focal spots is examined in detail; results are presented and compared with other criteria. Finally, a prescription for cascading elements into a system is given and applied to the case of magnification radiography.