Polishing of a 6.5 m f/1.25 mirror for the first Magellan telescope

We describe the optical fabrication and testing of the 6.5 m f/1.25 primary mirror for the first Magellan telescope. Figuring was performed with a 1.2m stressed lap, which bends under active control to match the local curvature of the optical surface, and a variety of small passive tools. The figure was measured with RI and visible interferometers, using refractive null correctors to compensate 810 microns of aspheric departure. After subtraction of Seidel astigmatism and spherical aberration, the finished mirror is accurate to 14 nm rms surface error, and has an encircled energy of 80 percent in 0.06 inch diameter at 500 nm.