Final optical design for the WEAVE two-degree prime focus corrector: Proceedings Volume 9147, Ground-based and Airborne Instrumentation for Astronomy V; 914773 (2014)

WEAVE is the next-generation wide-field optical spectroscopy facility for the William Herschel Telescope (WHT) in La Palma, Canary Islands, Spain. We present the final optical design for the two-degree Prime Focus Corrector (PFC) for the WHT optimised for WEAVE. The nominal optical design provides a polychromatic PSF that does not exceed 0.6 arcsec (80% encircled energy diameter) over a wavelength range from 370 to 1000 nm covering a two-degree field-of-view (FOV) for zenith angles up to 65 degrees. We describe the optical issues that had to be addressed prior to the Final Design Review (FDR) and present the trade-offs that were necessary between manufacturability and performance. We detail the results of an in-depth Monte Carlo simulation that contains all the manufacturing, alignment and stability issues that affect the PSF error budget of the Prime Focus Corrector. As a result of multiple iterations regarding the different tolerances of the system, the polychromatic PSF (80% encircled energy diameter) including all errors stays below the required 1 arcsec.