VST optics design strategy and foreseen performance from U to I bands

摘要

This paper shows criteria and strategy followed for the optics design of VST telescope, and foreseen image quality. The optics design has been optimized in order to achieve the high required image quality on the base of main scientific requirements, mechanics constraints coming from the wide CCD mosaic camera and dimensional requirements. Manufacturing reliability integrated operational efficiency, and costs optimization criteria have been also taken into account. The VST optics has been designed in order to have a 2.61 m Alt.az telescope operating from U to I bands with an excellent image quality (80% of Encircled Energy enclosed in less than two pixels) on a wide field of view (1° x 1°). The telescope will have a very high resolution (0.21 "/pixel) with a pixel size of 15 μm. The peculiarity of VST optics design is that telescope configuration is not a pure Ritchey - Chretien, but it is integrated with two different refracting correctors in order to minimize residual field aberrations. One corrector is optimized for observations at small zenith angles (U-I bands), while the other one includes an ADC providing high quality images until zenith angles of 50° (B-I bands). This corrector is a very useful and innovative integrated facility. The optics is being manufactured from Zeiss/LZOS. The telescope is going to be mounted in Napoli before shipment to Chile where it will be installed near the giants VLT units and will be a dedicated wide field imaging facility operating in narrow and wide visible bands.