 Beryllium mirrors are of particular interest . Large @-@ area mirrors , frequently with a honeycomb support structure , are used , for example , in meteorological satellites where low weight and long @-@ term dimensional stability are critical . Smaller beryllium mirrors are used in optical guidance systems and in fire @-@ control systems , e.g. in the German @-@ made Leopard 1 and Leopard 2 main battle tanks . In these systems , very rapid movement of the mirror is required which again dictates low mass and high rigidity . Usually the beryllium mirror is coated with hard <unk> nickel plating which can be more easily polished to a finer optical finish than beryllium . In some applications , though , the beryllium blank is polished without any coating . This is particularly applicable to cryogenic operation where thermal expansion mismatch can cause the coating to buckle . 
