Abstract: There is disclosed an optical assembly for viewing a scene. The optical assembly has an optical path extending from an objective end of the optical assembly to an eyepiece and is characterised by the provision of an electrochromic filter mounted within said optical path and an electrical control arrangement. The control arrangement is electrically connected to the electrochromic filter and is operable to adjust the optical transmittance of the electrochromic filter to thereby control the intensity of scene light which reaches the eyepiece along the optical path.