Comparing novel and conventional methods for optical system alignment using deflectometry

This paper compares two different ways of aligning optical systems using deflectometry: a novel method incorporating the sine condition test and deflectometry, and conventional multi-field points measuring deflectometry. The study aims to provide experimental evidence that the novel method is effective and has advantages over the conventional method. The experiment was carried out using a singlet as the unit-under-test with visible deflectometry composed of a camera and a monitor. In the conventional approach, the camera is moved to multiple field points to measure transmitted wavefront aberrations. For the accurate measurement of the aberrations, accurate knowledge of the camera positions is desired for conventional deflectometry. In the novel approach, the camera is fixed at an on-axis field point, while the monitor is moved to at least two positions in the longitudinal direction. Even if the camera is fixed, the new method can derive the linear behavior of aberrations over the field as it measures pupil mapping error and slope mapping error instead of wavefront error directly. Also, it is insensitive to positional errors in the monitor. This is made possible by discovering the complementary aspects of the sine condition test and deflectometry. We emphasize that the new alignment method is not performing two independent tests separately. The test can be done via one test setup requiring a camera and a monitor equivalent to a deflectometry system. The results demonstrate the benefits of the novel alignment method, which eliminates the need for accurate control of the test instrument movement during the alignment process.