Large mirror figuring and testing
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We describe a method for figuring and testing large aspheric mirrors using a rectangular, flexible lap (the so-called ‘Membrane Tool’) and a vibration stabilized interferometer. The rear side of the lap is covered with computer controlled dynamic pressure actuators which determine the amount of material to be removed for surface error correction. This method has been developed in the laboratory and tested to some extent by figuring thef/2.2 primary of the 3.6 m ESO-NTT. We describe the ongoing developments and the manufacturing plan for 8 m-class mirrors.
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