Centring Tester VP 30508

International standard ISO 10110 defines the centring error of a single optical lens or cemented lens as the surface tilt angle between the normal to its spherical surface and a reference axis such as the symmetry axis of the cylindrical edge of the optical element. Precise knowledge of the centring error is important as centring errors will have direct impact on the imaging quality of an optical assembly or subassembly. This also explains why centring error tolerances are specified for each lens in the design phase of any optical assembly.

Schneider-Kreuznach’s centring tester VP 30508 measures the centring error - in accordance with ISO 10110 - of single optical lenses or cemented lenses with diameters ranging from 5 to 200mm with unsurpassed accuracy. Therefore a small light spot is projected under a certain angle on to the surface of the rotating lens and the light reflected from that rotating lens’ surface is then detected by a CCD camera. A personal computer included with the system reads out the image from the CCD camera via a frame grabber card and the system software then calculates the centring error (or decentring) directly from the deflection of the reflected light spot. The instrument is equipped with both, an upper and a lower optical head. Single lens elements with two surface tilt angles therefore can be measured from both sides without the need to flip the lens in between.

Knowledge of the focal length or radius of curvature of the lens surfaces is not required. Hence, when testing different types of lenses there is no need to swap any relay lens as in case of the widely known autocollimator method and consequently there is virtually no changeover time. Due to the usage of a cast steel, highly rigid gantry and robust mechanical components the centring tester is well suited for usage on the production floor and is insensitive to subsonic noise and similar mechanical vibrations.

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