A varioscope optical unit has a positive member (9) with a positive refractive power and a negative member (11) with a negative refractive power arranged along an optical axis (OA) so that the negative member follows the positive member along an observation direction (B). At least one of the members is displaceable along the optical axis. Each member has a first termination lens surfaces (23, 27) counter to the observation direction (B) and second termination lens surface (25, 29) in the observation direction. The second termination lens surface of the positive member and the first termination lens surface of the negative member are concave when viewed in the observation direction (B) and have radii of curvature of at most 500 mm. The second termination lens surface of the negative member is convex when viewed in the observation direction (B) and has a radius of curvature of at most 70 mm.