2020/01/03 by Jeffrey K. Ratzloff, Ratzloff, Jeffrey K., Nicholas M. Law +6
Engineering · Physics and Astronomy · #Adaptive optics and wavefront sensing #Astronomy and Astrophysical Research #CCD and CMOS Imaging Sensors #FOS: Physical sciences #Instrumentation and Methods for Astrophysics (astro-ph.IM)
paper · pdf · doi:10.48550/arxiv.2001.00879
openalex publication_date 2020/01/03 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
Camera lenses are increasingly used in wide-field astronomical surveys due to\ntheir high performance, wide field-of-view (FOV) unreachable from traditional\ntelescope optics, and modest cost. The machining and assembly tolerances for\ncommercially available optical systems cause a slight misalignment (tilt)\nbetween the lens and CCD, resulting in PSF degradation. We have built an\nautomated alignment system (Robotilters) to solve this challenge, optimizing 4\ndegrees of freedom - 2 tilt axes, a separation axis (the distance between the\nCCD and lens), and the lens focus (the built-in focus of the lens by turning\nthe lens focusing ring which moves the optical elements relative to one\nanother) in a compact and low-cost package. The Robotilters remove tilt and\noptimize focus at the sub 10 micron level, are completely automated, take 2\nhours to run, and remain stable for multiple years once aligned. The\nRobotilters were built for the Evryscope telescope (a 780 MPix 22-camera array\nwith an 8150 sq.deg. field of view and continuous 2-minute cadence) designed to\ndetect short timescale events across extremely large sky areas simultaneously.\nVariance in quality across the image field, especially the corners and edges\ncompared to the center, is a significant challenge in wide-field astronomical\nsurveys like the Evryscope. The individual star PSFs (which typically extend\nonly a few pixels) are highly susceptible to slight increases in optical\naberrations in this situation. The Robotilter solution resulted in a limiting\nmagnitude improvement of .5 mag in the center of the image and 1.0 mag in the\ncorners for typical Evryscope cameras, with less distorted and smaller PSFs\n(half the extent in the corners and edges in many cases). In this paper we\ndescribe the Robotilter mechanical and software design, camera alignment\nresults, long term stability, and image improvement.\n