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VLT secondary mirror unit performance and test results

This paper explains the overall mechanical functions of the Very Large Telescope Secondary Mirror Unit (VLT-M2 Unit), and the method of their verification by tests inside two different test adapters. The cinematic mechanisms of the M2 Unit are the Focusing Stage, Centering Stage and the Chopping Assembly which enables to adjust the position of the secondary mirror along 5 degrees of freedom. All these mechanisms are characterized by very high stiffness and accuracy, long lifetime and high reliability. The presentation of the finally achieved performance test results of the M2 Unit, realized by their high precision mechanisms, are the major points of this presentation.