An optical assembly has at least one mirror with a mirror body. The latter is carried by a support body, which has a first support body portion and a second support body portion. An at least thermally separating region is arranged between the two support body portions. At least one surface portion of at least one of the support body portions or of a body thermally coupled thereto is modified in such a way that a thermal emission coefficient εm of the modified surface portion differs from a thermal emission coefficient εu of the unmodified surface portion by at least 10%. The result is an optical assembly, in which an improved thermal stability is achieved by the predetermining of the thermal emission coefficients.