  AKARI currently in space carries onboard a cryogenically-cooled lightweight
telescope with silicon carbide mirrors. The wavefront error of the AKARI
telescope obtained in laboratory measurements at 9 K showed that expected
in-orbit imaging performance was diffraction-limited at a wavelength of 6.2 um.
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 the
jettison of the cryostat aperture lid in the orbit, we observed a star with the
InfraRed Camera (IRC) onboard AKARI. Since the initial star images observed in
the near-infrared (IR) bands were significantly blurred, we twice moved the
secondary mirror for the focal adjustment based on the results of model
analyses as well as data analyses of the near-IR images. In consequence, we
have successfully adjusted the focus of the telescope. The in-orbit imaging
performance thus obtained for the AKARI telescope is diffraction-limited at a
wavelength of 7.3 um, slightly degraded from that expected from the laboratory
measurement.
