The mechanical design for the WEAVE prime focus corrector system

WEAVE is the next-generation, wide-field, optical spectroscopy facility for the William Herschel Telescope (WHT) in La Palma, Canary Islands, Spain. The WHT will undergo a significant adaptation to accommodate this facility. A two- degree Prime Focus Corrector (PFC), that includes an Atmospheric Dispersion Compensator, is being planned and is currently in its final design phase. To compensate for the effects of temperature-induced image degradation, the entire PFC system will be translated along the telescope optical axis. The optical system comprises six lenses, the largest of which will have a diameter of 1.1m. Now that the optical elements are in production, the designs for the lens cells and the mounting arrangements are being analysed to ensure that the image quality of the complete system is better than 1.0 arcsec (80% encircled energy diameter) over the full field of view. The new PFC system is designed to be routinely interchanged with the existing top-end ring. This will maximise the versatility of the WHT and allow the two top-end systems to be interchanged as dictated by the scientific needs of the astronomers that will use WEAVE and other instruments on the telescope. This manuscript describes the work that has been carried out in developing the designs for the mechanical subsystems and the plans for mounting the lenses to attain an optical performance that is commensurate with the requirements derived from planning the WEAVE surveys.