Quantitative measurement of Φ140mm F/2 parabolic surface with Ronchi grating test method

Three-dimensional shape measurement of large-aperture aspheric mirrors by off-axis null Ronchi test

“…It can be seen from Fig. 5 that there are no jagged edges on bands of null gratings, which exist on bands of the classical null Ronchi grating [6][7][8].…”

“…7, there are significant jagged edges. Using Malacara's method [6,8], we calculate the errors of the reconstructed surface. The maximum error is 6.3 × 10 −3 mm for the null Ronchi grating, and the maximum error for the null sinusoidal grating is as low as 5.2 × 10 −5 mm with our method, from which we can see that the null sinusoidal grating can avoid the influence of the jagged edges.…”

“…The shape measurement plays an important role in fabricating aspheric mirrors. Many methods, such as mechanical measurement, interferometry, phase measuring deflectometry (PMD) [1], and the Ronchi test [2][3][4][5][6][7][8][9][10], have been used to test aspheric mirrors. Among these methods, both the interferometer and the three-coordinate measuring machine can measure aspheric mirrors with high accuracy.…”

“…The Ronchi test is a very powerful candidate to quantitatively or qualitatively measure the degree to be corrected of an optical surface or lens since it is simple to operate and easy to interpret the experimental observations. According to whether fringes of a grating are curved, the Ronchi test is divided into the normal Ronchi test [2][3][4]10] and the null Ronchi test [7][8]. Compared with the normal Ronchi test, the null Ronchi test has some advantages.…”

“…The deviations of the mirror are restored by integrating, and then the three-dimensional (3D) shape of the mirror is reconstructed. Compared with the classical null Ronchi test [6][7][8], the method can provide enough measured data points on the surface under test by use of the null sinusoidal gratings, and it can eliminate jagged edges of bands on the null gratings by means of the phase information. Moreover, the use of the T-LCD screen makes it not only convenient to change period and direction of the curved fringes but also accurate to control phase shifting.…”