This is an optical/infrared telescope. It is a general purpose telescope. A segmented primary

mirror is adopted with diameter 12 m and f-ratio 1.6. This telescope has prime focus,

Cassegrain, Nasmyth and coud´e systems. The prime focus system has a 1.◦5 field-of-view

corrector with excellent image quality.

It will be used for multi-object fibre spectroscopic observation and CCD photography. In this 12-m telescope, all systems except the prime focus system share the same secondary mirror; the Nasmyth and coud´e systems are formed byadding relay mirrors; and the method of moving a secondary mirror is used to enhance image quality.

All these features originate from the innovative optical system of the Chinese 2.16-m telescope. At the Cassegrain focus, a dark object spectrograph, for example, can be installed

without any corrector; and in case a field of view is needed, a corrector may be added. Both

the Nasmyth and coud´e systems have exceptionally excellent image quality and the exchange between them occurs very conveniently. Many instruments in visible and infrared wavebands, some with an adaptive optics system, will be installed at the Nasmyth platform.

Coud´e system will be used for interferometry and for those instruments which require high stability. This configuration has a nearly full range of systems but it is not complex, and it can even be adopted by 20–40-m class telescopes.