Deflectometry with better Accuracy

Deflectometry is a technique to measure specular objects. The principle is simple and the local sensitivity is very high. The challenge is to achieve a very good global accuracy, which strongly depends on the quality of the calibration. During the last years a new calibration method was developed to reduce the global error: on a field of 80 x 80 mm a global trueness of about 1 µm (p-v) could be achieved, which is sufficient for many technical applications. Towards competition with interferometry, further improvement is necessary. We demonstrate one novel option by exploiting that the calibration errors are independent of an object rotation. We combine measurements taken from several different object orientations. On a field of 20 x 20 mm we already achieved a p-v trueness of 110 nm, while the trueness from only one single orientation is 600 nm (p-v).