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Proceedings Paper

Dome flat-field system for 1.3-m Araki Telescope
Author(s): Tomohiro Yoshikawa; Yuji Ikeda; Naofumi Fujishiro; Shunsuke Ichizawa; Akira Arai; Mizuki Isogai; Atsunori Yonehara; Hideyo Kawakita
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Paper Abstract

We report the system/optics design and performance of the dome flat-field system for the Araki Telescope, a 1.3- m optical/near-infrared telescope at Koyama Astronomical Observatory in Japan. A variety of instruments are attached to the telescope. The optical imager, which is intended to search for exoplanets, requires an illumination flatness within 1% on the focal plane over the 17-arcmin FOV. Illumination flatness at both the pupil plane and the focal plane of the telescope is essential for calibration of the transmittance of the optical system. We devised an optical design for the flat-field system that satisfies illumination flatness at both the focal and pupil planes using the non-sequential ray tracing software LightTools. We considered far-field illumination pattern of the lamps, scattering surface reflectance distribution of the screen, telescope structure, primary/secondary mirrors, and mirror baffles. We achieved a flat illumination distribution of 0.9% at the focal plane. The systems performance was tested by comparison with a cloud-flat frame, which was derived by imaging cloud cover illuminated by city lights. The calibration data for the dome flat-field system agree well with the cloud-flat frame within 1% for the g′ and i′ bands of the imager, but the r0 band data does not meet the requirement (less than or equal to 2). Moreover, various instruments require a focal plane illuminance ranging over three orders of magnitude. We used six high-power (60W) halogen lamps; the output power is remotely controlled by a thyristor-driven dimmer and a bypass circuit to an autotransformer.

Paper Details

Date Published: 17 September 2012
PDF: 9 pages
Proc. SPIE 8444, Ground-based and Airborne Telescopes IV, 84446G (17 September 2012); doi: 10.1117/12.925428
Show Author Affiliations
Tomohiro Yoshikawa, Koyama Astronomical Observatory, Kyoto Sangyo Univ. (Japan)
Yuji Ikeda, Koyama Astronomical Observatory, Kyoto Sangyo Univ. (Japan)
Naofumi Fujishiro, Koyama Astronomical Observatory, Kyoto Sangyo Univ. (Japan)
Shunsuke Ichizawa, Cybernet Systems Co., Ltd. (Japan)
Akira Arai, Koyama Astronomical Observatory, Kyoto Sangyo Univ. (Japan)
Mizuki Isogai, Koyama Astronomical Observatory, Kyoto Sangyo Univ. (Japan)
Atsunori Yonehara, Koyama Astronomical Observatory, Kyoto Sangyo Univ. (Japan)
Hideyo Kawakita, Koyama Astronomical Observatory, Kyoto Sangyo Univ. (Japan)

Published in SPIE Proceedings Vol. 8444:
Ground-based and Airborne Telescopes IV
Larry M. Stepp; Roberto Gilmozzi; Helen J. Hall, Editor(s)

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