Abstract: The optical system includes a point source of monochromatic light which is focused by a first lens onto a frequency plane. A pair of transparencies bearing information in a single-axis density-modulated form are interposed before the frequency plane. The transparencies may be arranged so that the information axis of one is angularly displaced 90.degree. relative to the information axis of the other. A slit is placed at the frequency plane at a 45.degree. angle relative to the axes of the transparencies so that the only light transmitted beyond the frequency plane is that which is passed through the slit. The light passing through the slit is focused by a second lens onto an image plane; and the resulting output image (read parallel to the direction of elongation of the slit) is the mathematical convolution or correlation function of the input signals, depending on whether the slit is placed at a +45.degree. angle or a -45.degree. angle.