Transition imaging phase measuring deflectometry for high-precision measurement of optical surfaces

• The transition imaging phase measuring deflectometry is proposed to overcome the convolution effect caused by the screen defocusing. • The screen and the surface under test can be focused at the same time to physically overcome the “position-angle uncertainty” problem. • The geometrical calibration of the measurement system requires only one-shot. • The measurement accuracy is improved by 5.8 times compared with the conventional method. The phase measuring deflectometry is a powerful measuring method for optical freeform surfaces, but the surface under test (SUT) and the screen pattern cannot be in-focus simultaneously. The defocusing of the screen in the imaging system can cause serious convolution effect. Then the mismatching errors arising in the phase demodulation will reduce the measurement accuracy. To solve this problem, the transition imaging phase measuring deflectometry is proposed. An auxiliary focusing mirror is applied to image the screen pattern to the position of the SUT, so that the camera can clearly capture the images of the screen pattern and the SUT at the same time. The system design, the geometrical calibration, and the fast solving method of the gradient field are developed. Finally, the measurement accuracy of the proposed method is experimentally demonstrated and it can be improved by 5.8 times when measuring complex surfaces.