A study is made of the effect of diffraction on imaging a square-wave object (in intensity) in incoherent light for slit and circular apertures suffering from spherical aberration. A modification of the usual Fourier series representation of the square wave is required to eliminate the unwanted Gibbs phenomena. The modulation of the image of the square wave is calculated by using transfer-function theory. Numerous examples are presented.
RICHARD BARAKAT and AGNES HOUSTON, "Modulation of Square-Wave Objects in Incoherent Light. I," J. Opt. Soc. Am. 53, 1371-1372 (1963)