The vignetting field stop procedure: A new physical measurement principle for the Deflectometric acquisition of big Optical Surfaces - DaOS

In the field of precision optics interferometry is often used to determine shape errors of optical surfaces, but especially for large convex optics or aspheres, it is strongly limited. The vignetting field stop procedure uses a Deflectometric approach to acquire big Optical Surfaces – DaOS. Instead of a sharp picture, a mathematically describable, defocused light spot caused by vignetting is determined. Thereby nearly any curvature of the specimen, even if the sign of curvature is changing, is measurable. By the vignetting field stop procedure photometric effects influences the linearity at different distances. Therefore suitable methods of calibration for the sensor are examined. Additionally the deflectometric setup is described. Furthermore the technical principle of deflectometric measurements using an angle detecting device is explained inclusive of random and systematic errors. Actual result of measurements with calculated absolute deviation of errors with a large lateral dimension as well as the determination of the maximal achievable lateral resolution by detecting mid frequent structures on flat and spherical test parts with a diameter of 300 mm are examined.