The invention relates to a mirror (1), for use in optical imaging systems, whereby the mirror is connected at the edge thereof to a reinforcing element (3), at least partly surrounding the mirror and the reinforcing element also fixes the relative position of the mirror with regard to a further optical element (4). Positioning means (5) are arranged on the reinforcing element, cooperating with positioning means (7), arranged on further optical elements. The optical imaging system in particular concerns a telescope for optical transmission techniques.