In-orbit focal adjustment of the AKARI telescope with Infrared Camera (IRC) images

Hidehiro Kaneda, Woojung Kim, Takashi Onaka, Takehiko Wada, Yoshifusa Ita, Itsuki Sakon, Toshinobu Takagi

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31 Citations (Scopus)


AKARI, currently in space, carries onboard a cryogenically cooled light-weight telescope with silicon carbide mirrors. The wavefront error of the AKARI telescope, obtained in laboratory measurements at 9 K, showed that the expected in-orbit imaging performance was diffraction-limited at a wavelength of 6.2 μm. The AKARI telescope has a function of focus adjustment by shifting the secondary mirror in parallel to the optical axis. On the 4th day after jettison of the cryostat aperture lid in orbit, we observed a star with the Infrared Camera (IRC) onboard AKARI. Since the initial star images observed in the near-infrared (NIR) bands were significantly blurred, we twice moved the secondary mirror for a focal adjustment based on the results of model analyses as well as data analyses of NIR band images. As a consequence, we successfully adjusted the focus of the telescope. The thus-obtained in-orbit imaging performance for the AKARI telescope is diffraction-limited at a wavelength of 7.3 μm, slightly degraded from that expected from laboratory measurements.

Original languageEnglish
Pages (from-to)S423-S427
JournalPublication of the Astronomical Society of Japan
Issue numberSPEC. ISS. 2
Publication statusPublished - 2007


  • Infrared: general
  • Techniques: image processing
  • Telescopes


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