Accurate measurement of centration of aspheric lenses or even freeforms is a challenge for most devices in optical manufacturing. We are providing a new attempt by combining an autocollimation device and a Vignetting Field Stop [1, 2, 3] device to measure lens centration and sagittal surface profile in a deflectometric approach. Both devices work independently at high accuracy. This presentation explains the technical setup, consisting of an autocollimation sensor (ELWIMAT-AKF) and a Vignetting Field Stop Sensor (ELWIMAT V-SPOT), which is mounted together with an air bearing rotary table in a vertical arrangement. Secondly, we provide the results of the centration measurement and the results from the surface reconstruction and slope error from the measured sagittal angle deviations. Finally, the results from a measured asphere (High Level Expert Meeting HLEM sample #3) is critically discussed to state the accuracy and applicability of the proposed measurement attempt.
In-situ measurements of complex surfaces during the polishing process is a challenge for the production of aspheric surfaces or freeforms. We are providing a new attempt by using a scanning deflectometric device based on our recently published DaOS [1] principle, which allows in-situ measurements of large optical surfaces in realistic production environments and offers the conditions for direct intervention and correction in the polishing process. The results of insitu surface measurements after three polishing steps of a large glass substrate (320 mm in diameter) in a lever-polishing machine (NLP500 from Stock Konstruktion GmbH) are shown and critically compared with interferometric measurements on a SSI-A Interferometer. In this paper, the technical setup consisting of a highly precise scanning penta prism device and a Vignetting Field Stop (VFS) Sensor is explained. Secondly, we are discussing the mathematical algorithm to reconstruct the complete surface from angle measurements from a given number of cross-sectional cuts. The data of the surface reconstruction are transformed into a XYZ-file format to be analyzed with MetroPro®. The results are shown and discussed in terms of accuracy and reproducibility. Finally, a comparison with interferometric measurements on an SSI-A (QED) at TH Deggendorf (THD), Technology Campus Teisnach is shown to proof the degree of accuracy and applicability of our new, fast and reliable device for in-situ measurements of complex surfaces.
The basic physical measurement principle in DaOS is the vignettation of a quasi-parallel light beam emitted by an expanded light source in auto collimation arrangement. The beam is reflected by the surface under test, using invariant deflection by a moving and scanning pentaprism. Thereby nearly any curvature of the specimen is measurable. Resolution, systematic errors and random errors will be shown and explicitly discussed for the profile determination error. Measurements for a “plano-double-sombrero” device will be analyzed and reconstructed to find out the limit of resolution and errors of the reconstruction model and algorithms. These measurements are compared critically to reference results that are recorded by interferometry and Deflectometric Flatness Reference (DFR) method using a scanning penta device.
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