Abstract: The primary mirror for the Multiple Mirror TelescopeConversion is the first 6.5 m honeycomb sandwich mirrorcast and polished by the Steward Observatory MirrorLab. We describe the optical fabrication and testing ofthe f/1.25 paraboloid, and present the finalmeasurements of figure accuracy and inferred imagequality. Figuring was performed with a 1.2 m stressedlap - which bends under active control to match thelocal curvature of the optical surface - and a varietyof small passive tools. The mirror was pressurized tocompensate for polishing loads and thereby eliminateprint-through of the honeycomb structure. The netresult is a smoother surface on scales of 5 - 20 cmthan has been achieved on previous honeycomb sandwichmirrors. The figure was measured with IR and visibleinterferometers, using refractive null correctors tocompensate 810 microns of aspheric departure. The finalmeasurements were used to calculate synthetic stellarimages in a variety of seeing conditions.!10
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