An objective with two lens elements has a first fully-reflective plane mir between the lens elements, and a second such mirror between the objective and a detector. The outermost lens element and the first mirror are carried in a housing rotatable with respect to another housing carrying the other lens elements and the second mirror. The other housing is rotatable about an axis between the second mirror and the detector. The system may thus do elevation scanning by rotating the first housing, and azimuth scanning by rotating the two housings about the mentioned axis. Image stabilization is accomplished by appropriately stabilizing one or both mirrors.