an optical system includes a housing having an axis of elongation , and a non - spherical window affixed to the housing . an optical corrector , preferably in the form of an aspherical strip of transparent material , is positioned adjacent to the curved inner surface of the window . the optical corrector is mounted on an optical corrector support , which is rotatable about the axis of elongation . an optical rain is positioned such the the optical corrector lies between the window and the optical train . the optical train includes at least one optical element operable to alter an optical ray incident thereon , and a gimbal upon which the at least one optical element is mounted . the gimbal is pivotable about a transverse axis perpendicular to the axis of elongation . the optical train is mounted on an optical train support , which is movable independently of the optical corrector support . a sensor is positioned to receive the optical ray passing sequentially through the window , the optical corrector , and the optical train .