Recent results of research in circuit theory and optics are combined to show both upper and lower bounds on the modulus of the transfer function of incoherent optical systems. The results are shown in the form of graphs. The upper bound is the best possible, but the lower has not been shown to be the greatest lower bound.
B. P. HILDEBRAND, "Bounds on the Modulation Transfer Function of Optical Systems in Incoherent Illumination," J. Opt. Soc. Am. 56, 12-13 (1966)