An optical assembly includes an optical element (13), configured in particular for the reflection of EUV radiation (4), and a protective element (30) for protecting a surface (31) of the optical element (13, 14) from contaminating substances (P). The protective element (30) has a membrane (33a-c) and a frame (34) on which the membrane (33a-c) is mounted. The membrane is formed by a plurality of membrane segments (33a, 33b, 33c) which respectively protect a partial region (T) of the surface (31) of the optical element (13) from the contaminating substances (P). The optical assembly can form part of an overall optical arrangement, for example an EUV lithography system.