The effect of defocusing on the diffraction images of a general periodic triangular-wave object has been investigated for the case of a narrow rectangular aperture. Results in the form of curves have been given for irradiance distribution and contrast in the images. The aperture has been assumed to be illuminated incoherently. A close similarity has been shown between the sine-wave response and triangular-wave response of a particular object function.
K. SINGE and K. N. CHOPRA, "Images of an Incoherent Triangular-Wave Pattern by a Slit Aperture in the Presence of Defocusing," J. Opt. Soc. Am. 59, 1639-1644 (1969)