CANGAROO-III is an Imaging Atmospheric Cherenkov Telescope (IACT) array of four 10 m telescopes for very high energy (sub-TeV) gamma-ray astronomy. A design study of Preprint submitted to Elsevier Preprint 24 October 2018 the CANGAROO-III telescope system was carried out using the Monte Carlo technique in order to optimize the pixel size and the telescope spacing. Studies were also made of observations at low elevation angles.

A new imaging atmospheric Cherenkov telescope with a light-weight re ector has been constructed. Light, robust, and durable mirror facets of containing CFRP (Carbon Fiber Reinforced Plastic) laminates were developed for the telescope. The re ector has a parabolic shape (f/1.1) with a 30 m 2 surface area which consists of sixty spherical mirror facets. The image size of each mirror facet is 0 .08 (FWHM) on average. The attitude of each facet can be adjusted by stepping motors. After Preprint submitted to Elsevier Preprint 26 May 2 0 0 0 the rst in situ adjustment, a point image of about 0 .14 (FWHM) over 3 degree eld-of-view was obtained. The e ect of gravitational load on the optical system was con rmed to be negligible at the focal plane. The telescope has been in operation with an energy threshold for gamma-rays of < 300 GeV since May 1999.

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