Optomechanical tolerancing of VISTA field corrector

摘要

VISTA is a 4m class survey telescope designed to perform pre-planned, ground-based astronomy surveys of the Southern sky in the visible and infrared spectrum. The telescope includes a Cassegrain mounted infrared (IR) camera with a field of view of 1.65 degrees. The camera has no cold stop, and therefore the three lenses constituting the field corrector are positioned inside the cryostat of the camera. A window of 950mm diameter closes the cryostat. The lenses have a diameter of approximately 600 mm, and the third lens have its first surface with an aspheric profile. The large cryostat window and the aspheric surface of the third lens are the most difficult components to manufacture and test. To our knowledge, they are the largest Infrasil 302 components to be mounted and used inside a cryostat at 100K up to this date.