The best diameter determination of the pin aperture in inverse Hartmann surface form measurement system

In the inverse Hartmann surface form measurement, the pin aperture selects light reflected from the test surface and determines the measurement resolution. The diameter of the pin aperture has influence on the size of light spots on CCD and the accuracy of determining the ray location on the pupil. The Fourier transform expression for precisely calculating the pin aperture diameter is derived from diffraction optics theory. Moreover, an estimation formula which directly calculates the diameter of the pin aperture is also derived. Simulation and experiment show that the fast estimation formula can meet the accuracy and effectively save time when calculate the best diameter of the pin aperture in real measurement.