A scanning telescope including an on-axis four-mirror reflective telescope configured to receive electromagnetic radiation through an optical aperture and to direct and focus the electromagnetic radiation onto an imaging detector, the on-axis four-mirror reflective telescope including a rear-most mirror configured to be movable over a range of angular tilt relative to an optical axis of the scanning telescope to scan a field of view of the imaging detector over a scan range. In one example, the rear-most scanning mirror is the tertiary mirror of the four-mirror reflective telescope, and all four mirrors are axisymmetric about the optical axis of the telescope.