Accurate Deflectometry for non-cooperative Applications

Deflectometry is a simple technology – in principle. The real challenge of quantitative deflectometry is calibration and evaluation. The difficulties dramatically rise with the size of the object and its slope dynamics. Not enough, online measurements within limited working space don’t allow for an optimal sensor geometry. So, even with sophisticated calibration there will be residual errors, depending on the i n d i v i d u a l object geometry. We will discuss how to overcome this serious problem of deflectometry. We exploit one new feature of our ‘holistic’ calibration [DGaO annual report 2011]: the calibration delivers not only the shape but the precise position and orientation of the object as well. We use this first iteration to re-calculate the rays from each pixel via the pupil and the object to the light source. With this information we are able to calculate significantly improved shape data. Thus, individual errors depending on the object are corrected. So, even objects with steep slopes can be measured with high trueness. We will demonstrate measurements within the limited working space of a diamond turning machine and of 1.2 m mirrors within a climate chamber.