A Mersenne reflector system using parabolic troughs as primary and secondary reflectors, in Cassegrainian and Gregorian configurations, and a Mersenne-like reflector system using truncated parabolic troughs as primary and secondary reflectors in the Cassegrainian configuration, using a variety of combinations of reflector shapes: elliptical primary and circular secondary, rectangular primary and square secondary, elliptical primary and square secondary, and rectangular primary and circular secondary. A method for constructing truncated Cassegrainian systems using truncated troughs.