Fabricating and testing of the trim plate for the Zwicky Transient Facility

摘要

The Zwicky Transient Facility (ZTF) is a new time-domain survey project that will use a new camera with a 47 square degree field of view mounted on the Samuel Oschin 48-inch Schmidt telescope. To achieve good image quality over all sixteen 6K*6K CCDs (386mm *395 mm corner to corner), a trim plate was added in front of the existing cemented achromatic doublet to form an air-spaced triplet corrector. The trim plate is a Schmidt corrector using fused silica with 1348mm in diameter but only 15mm in thickness. The plate has been completed at NIAOT and already been mounted to the ZTF, the PSF seems very good. The detailed fabrication process and testing to the trim plate from fine grinding to finish are presented in this paper, which includes CMM test, NULL test design, and Computer Controlled Polishing process developed at NIAOT.