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Update on the 3.5-m WIYN Mirror Project (1Jun92) (from KPNO, NOAO Newsletter No. 30, 1 June 1992) The 3.5-m WIYN mirror is scheduled for delivery at the telescope by February 1994. The mirror has already been polished to a superbly accurate spherical surface, but must still be ground and polished to an asphere, and then aluminized. For the last 18 months we have been testing the thermal control system and the active support system. Testing will continue for another month or so. Meanwhile mechanical drawings for the flexible bar lap, which will be used for first grinding and then polishing the optical surface of the 3.5-m mirror to its final aspheric configuration, are being released for fabrication. The design of the control system for the actuator in the lap is well along and will be tested with the prototype lap soon. Two null lens assemblies are needed for optical testing while we generate the asphere. An IR null lens, which allows measurements on an unpolished surface, will be used during the grinding phase in conjunction with a Hartmann screen. During polishing a visible null lens will be used, also in conjunction with a Hartmann screen test. The mechanical design of these null lens assemblies is underway. Wayne Pollard, Michael Merrill
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