In phase-shifting point diffraction interferometry (PS/PDI), a pinhole with a diameter of 34 nm is necessary to measure a wave-front aberration of extreme ultraviolet projection optics of numerical aperture (NA) 0.20. However, it is extremely difficult to process such a small pinhole, and light transmission through the pinhole becomes too low. Here, the diameter of a pinhole is optimized, together with the thickness of a Ta membrane, for a converging wave of NA 0.20 with no aberration so that the difference between a wave front produced by the pinhole and that of a spherical wave is minimized. On that condition, the optimum values are a diameter of 50 nm and a thickness of 200 nm. For these values, behaviors are examined in real cases, including focal point shifts and aberrations with incident light. Astigmatism in the aberrations has the most impact on a wave-front error, and a 0degrees-90degrees astigmatism (Z5) coefficient in the FRINGE Zernike polynomials of test optics is required to be less than 50 mlambda to use the pinhole in PS/PD1. For optics with a higher NA (similar to0.25), the use of a Ta membrane is not adequate because of poor performance in small pinholes, and materials that have higher extinction coefficients are preferable. (C) 2004 American Vacuum Society.