26 May 2011 Complete characterization of assembled optics with respect to centering error and lens distances
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Abstract
The position of optical surfaces and elements in the final assembly of an optical system has a strong influence on the imaging quality of the system. After the assembly of the complete optics is finished it is difficult to check the centering error and the distances of the single optical elements. We will describe a technique to measure the lateral displacement of each centre or curvature with respect to a given reference axis with 0.1 micron accuracy. Additionally it is possible to measure the distances between surfaces of the assembled optics with an accuracy of 1 micron. The measurement is based on the combination of a focusing autocollimator and a short coherent interferometer. The measurement is non-destructive and can be applied to optical systems with several optical elements (approx. 20 lenses). Both the focusing autocollimator and the short coherent interferometer are working independently. It will be shown that a combination of these methods improves the feasibility and accuracy of both methods. In general the method can be applied to optical systems based on spherical surfaces. As far as the paraxial area is considered, the use of this method can be also extended to systems with aspherical surfaces. The restriction is that these measurements will only provide the information of the lateral displacements of the paraxial centres of curvature and the distances between the optical surfaces. The tilt of the aspherical axis is not revealed by this technique. But with the use of an additional optical distance sensor and a special quality control strategy the tilt of each aspherical axis in the assembled optical system can be determined. The quality strategy requires some preliminary measurements of the single optical elements before assembly. Applications mainly include the measurement of cell phone and digital camera lenses. However, any type of objective lens from endoscope up to very complex objective lenses used in microlithography can be measured with highest accuracy. Measurement results of different samples will be provided and discussed.
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J. Heinisch, J. Heinisch, P. Langehanenberg, P. Langehanenberg, H. Pannhoff, H. Pannhoff, } "Complete characterization of assembled optics with respect to centering error and lens distances", Proc. SPIE 8082, Optical Measurement Systems for Industrial Inspection VII, 80821M (26 May 2011); doi: 10.1117/12.889561; https://doi.org/10.1117/12.889561
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