Abstract: An optical system utilized to provide guidance information in the form of a modulated beam for a beamrider missile during its rocket powered flight phase. Our system comprises first and second zoom type optical subsystems arranged to function cooperatively in object space, utilizing coincident lines of sight, with these optical subsystems serving to provide guidance information to the missile when the exhaust plume from its rocket engine is relatively difficult to penetrate. The first optical subsystem is utilized in a closed loop servo system for positioning a mirror gimballed about two axes, such that it continuously tracks the missile. The second optical subsystem, along the optical axis of which the modulated beam is directed, comprises a negative optical group and a positive optical group combined into a defocusable beam expander.