We recently published this new paper at the occasion of SPIE Optifab in Rochester (NY) mid October 2023 (we exhibited our product and technology and held a conference). The conference room was nearly full. Our presentation raised a strong interest in the audience and we had many interested questions, it was a real pleasure. So for those who could not attend, here is the abstract.
Deflectometry (shape measurement of a mirror from the distortion of the image of a monitor screen displaying fringes) has been known for a long time, but suffers from intrinsic features that make accurate absolute measurements very difficult. In particular, all the metrological quality depends on the ultra precise identification of the system geometry: ray trajectories in the object space, shape of the monitor screen, position of this screen and position of one point of the measured object, all these in the camera frame of reference. We present an instrument that permits all these identifications in a simple push-button way. The fundamental ambiguity of deflectometry (a single measurement may correspond to an infinite number of object shapes, due to the unknown constant after slopes integration) is raised with our patented coaxial deflectometry approach: two measurements are made with an axial movement of the camera, and only one shape is compatible with these two measurements.
We present the identification methodology of the system, and results for absolute measurements of spheres, aspheres and freeforms, within a λ/40 accuracy, with some comparisons with results obtained with a Taylor-Hobson LUPHOScan®.
Keywords: Deflectometry, metrology, freeform
Feel free to ask for the full abstract if interested.