But let's come to the main mirror (Fig. 5) which, as we said, it is made up of a certain number of tiles. Specifically, the mirror consists of 18 tiles organized in three rings (Fig. 6), each made up from 6 mirrors. The mirrors that make up each ring have identical optical characteristics each other but different from those of the mirrors of others rings. The individual tiles are mounted on the structure of the telescope by means of triangular supports. One of the vertices of the triangle is fixed while on the other two motors are mounted, called actuators, which allow you to perform tip / tilt movements of the mirror. By appropriately moving the actuators, it is possible to align all the mirrors with each other, so that the primary mirror takes the required shape from the optical design, behaving in fact like a monolithic mirror. Actuators allow also to maintain the alignment of mirrors and thus the shape of the mirror surface primary to varying external conditions (ambien...