A method and apparatus for designing an iris biometrics system that operates in minimally constrained settings. The image acquisition system has fewer constraints on subjects than traditional methods by extending standoff distance and capture volume. The method receives design parameters and provides derived quantities that are useful in designing an image acquisition system having a specific set of performance requirements. Exemplary scenarios of minimally constrained settings are provided, such as a high volume security checkpoint, an office, an aircraft boarding bridge, a wide corridor, and an automobile.