Optical design of the Advanced Camera for Surveys, a third generation HST axial science instrument

Robert A. Woodruff and Raymond F. Cahill (BATC)

The Advanced Camera for Surveys, designed to be installed in 1999 during the third servicing mission of the HST, is a high performance, multi-spectral, axial bay camera.

The design provides three wide-band cameras plus coronagraphic capability. The cameras cover the spectral region from 115 nm to 170 nm and from 200 nm to 1000 nm. They are the very wide FOV (200 by 204 arc sec) WFC camera, the wide FOV (26 by 29 arc sec) HRC camera, the wide FOV (26 by 29 arc sec) SBC ultraviolet, and the coronagraph which uses the HRC CCD. Numerous filters are provided for each of the three cameras using only three filter wheels, two of which are shared by the WFC and HRC. The optical design uses heritage from STIS, a third generation HST instrument. To achieve full wavelength coverage the designs are all-reflective. The FOV of the two-mirror STIS design is extended for the WFC by use of a reflective Schmidt-like plate as a third mirror. The filters are placed in the corrected converging beam and are OPD-matched to maintain focus. Protected silver reflective coatings are used on the WFC mirrors to maximize throughput and minimize polarization sensitivity.

The paper will describe the optical design and compare predicted performance with measured performance. The use of error budgets during the design process will also be discussed.

Key Words: (< 5) aberration correction, extending field of view, optical system design

Brief Biography, Principal Author:

Robert Woodruff has 33 years of experience designing spaceborne optical systems on projects including Skylab, Nimbus, Apollo-Soyuz, Galileo, SIRTF, microgravity, Hubble Space Telescope and NGST. He is the principal designer of the Advanced Camera for Surveys, a third generation HST instrument, the HST Space Telescope Imaging Spectrograph and the Goddard High Resolution Spectrograph.

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