An unconventional manner to keep centered the thin main mirror of the EPSILON Telescope of the C.2.P.U.

The new project was called C.2.P.U. (Centre Pédagogique Planète et Univers) and is now dedicated mainly to astronomical and astrophysical research. The old mirrors were discarded because they were cut to observe exclusively in the infrared, and were replaced by new mirrors obtained by reworking, for economic reasons, two 105 cm diameter Zerodur discs existing at the O.C.A. that had been set aside at the end of the project for which they were used. After the optical work was completed, both mirrors were of excellent quality, but one of them, obtained from a plane-convex Zerodur disc, had a meniscus-shaped blank and was relatively thin (62 mm for a total weight of about 140 kg).The intervention, proposed to reduce the astigmatism introduced in the optics consists of replacing the lateral supports that defined the centering of the mirror with a mechanism that supports the mirror from the central hole present in the mirror. This solution made it possible to greatly reduce astigmatism, improving the optical quality of the observations. The article will present the analyses and results before and after the modification.