Manufacturing the Schmidt corrector lens for the Pierre Auger Observatory

The Pierre Auger Observatory is designed to provide measurements of Extensive Air Showers initiated in the upper atmosphere by cosmic rays with energies greater than 1018 eV. One of the employed techniques is air fluorescence detectors with UV filters and a corrector lens. We describe in this article the production process of the corrector lens in Brazil, starting from the design of the machines up to the final tests in the prototype telescope. We have used diamond grinding tools to shape a ring of corrector lens with inner radius of 85 cm and outer radius of 110 cm, divided in 24 segments and with aspherical shape. After the production of a first complete set of segments, we measured a segment shape scanning with a laser. The lens was then installed at the telescope and we measured its overall influence on the spot size, taking pictures of the Vega star