An overview of the Seimei telescope, a 3.8 m optical infrared telescope located on Mt. Chikurinji in the Okayama prefecture of Japan, is presented. Seimei is a segmented-mirror telescope whose primary mirror consists of 18 petal-shaped segments. The telescope tube supporting the thin segmented mirrors is structurally incorporated within large arc-rails providing the elevation axis. The tube has a light-weight homologous structure designed with a genetic algorithm. The total weight of the telescope tube, including 1.4-ton optics, is only 8 tons. By virtue of its light weight, the telescope is able to point at an object anywhere in the observable sky within one minute. The telescope is operated by Kyoto University in collaboration with the National Astronomical Observatory of Japan (NAOJ). Half of the telescope time is used by Kyoto University. The remaining time is open to the Japanese astronomical community. NAOJ is responsible for the management of the open-use time, including handling of the observation proposals. The telescope is now regularly performing scientific observations on the basis of a variety of proposals.

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A segmented mirror system is essential to realize extremely large telescopes. In this paper, we discuss the conceptual design for the control system of the segmented primary mirror in the SEIMEI telescope employing 18 segments, 72 sensors, and 54 actuators. Two types of control algorithms, Centralized Control System (CCS) and Distributed Control System (DCS), are presented. CCS drives all the segments by integrated information of all sensors and DCS drives each segment by individual information of local sensors, and they are expected to play complementary roles. The effectiveness of CCS and DCS are demonstrated by numerical simulations.

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