The utility and elegance of the Modulation Transfer Function (MTF) in photo-optical system design is well known. The difficulties involved in the measurement of this performance criteria, however, have restricted its practical application. The relationship between MTF and several of the more easily measured and specified resolution criteria, such as point and line spread functions, knife edge response, and encircled energy, is developed. A method of specifying resolution criteria determined by MTF analysis for the optical designer and the evaluation laboratory, is presented. The practicality of the method is enhanced by introducing certain simplifications to reduce the time required for computation.