The corrector is designed to provide a larger field of view to the focal plate, allowing 5,000 fibers to be arranged over 8 square degrees.
The design includes four large lenses composed of fused silica. The two smaller lenses are aspheric on one surface; all other silica surfaces are spherical. Multiple vendors were able to meet the stringent specifications required for DESI’s lenses. An atmospheric dispersion compensator (ADC) is included in the design, in order to meet blur requirements at off-zenith angles. This compensator includes two large wedged borosilicate lenses with spherical surfaces.
The corrector design provides a linear field of view of 3.2 degrees, corresponding to a diameter of about 812 millimeters at prime focus and an area of 8 square degrees.