A folded optical system is provided in the form of a telescope (20) for viewing distant objects. At least two optical elements (22, 24) have curved surfaces (32, 34) for imaging rays of radiation from a distant object. The two surfaces are positioned so as to permit a series of reflections therebetween for magnification of the resulting focal length of the optical system and diminution in the overall viewing angle so as to attenuate any light which may emanate from sources of radiation disposed off an optical axis which intercepts the object being viewed. One or more of the optical elements may be provided with apertures (30) through which rays of radiation are directed to a sensor (26) of the radiation, the sensor being positioned on a image plane to receive an image of the objects being viewed. First and second ones of the optical surface may be concave and convex, respectively, or alternatively, each optical surface may be concave with a folding mirror being utilized in the reflection of rays therebetween. One or more of the optical surfaces (32), or the surface of the folding mirror is fabricated as a set of zones (36) on a common substrate wherein each zone is utilized solely in the performance of one set of reflections in the series of reflections of the rays. Thereby, each zone can be separately configured for compensation of any aberrations and for clarifying the resulting image.