A zoom optical system comprising: a light source configured to illuminate an object located in an object plane; a compensator lens group, optically coupled to the object, having a first positive optical power, configured to move relative to the object plane , and comprising six lenses (230, 232, 234, 236, 238, and 239), which comprise positive, negative, positive, positive, negative, and positive power lenses, listed in sequence beginning with the lens closest to the object plane; a variator lens group, optically coupled to the compensator lens group, having a negative optical power, configured to move relative to the object plane and the compensator group, and comprising three lenses , which comprise positive, negative, and negative power lenses, listed in sequence beginning with the lens closest to the object plane; and an objective lens group, optically coupled to the variator lens group, having a second positive optical power, configured to remain in a fixed position relative to the object plane and to project an image of the object, and comprising three lenses , which comprise negative, positive, and positive power lenses, listed in sequence beginning with the lens closest to the object plane. a light source configured to illuminate an object located in an object plane; a compensator lens group, optically coupled to the object, having a first positive optical power, configured to move relative to the object plane , and comprising six lenses (230, 232, 234, 236, 238, and 239), which comprise positive, negative, positive, positive, negative, and positive power lenses, listed in sequence beginning with the lens closest to the object plane; having a first positive optical power, configured to move relative to the object plane , and comprising six lenses (230, 232, 234, 236, 238, and 239), which comprise positive, negative, positive, positive, negative, and positive power lenses, listed in sequence beginning with the lens closest to the object plane; a variator lens group, optically coupled to the compensator lens group, having a negative optical power, configured to move relative to the object plane and the compensator group, and comprising three lenses , which comprise positive, negative, and negative power lenses, listed in sequence beginning with the lens closest to the object plane; and having a negative optical power, configured to move relative to the object plane and the compensator group, and comprising three lenses , which comprise positive, negative, and negative power lenses, listed in sequence beginning with the lens closest to the object plane; and an objective lens group, optically coupled to the variator lens group, having a second positive optical power, configured to remain in a fixed position relative to the object plane and to project an image of the object, and comprising three lenses , which comprise negative, positive, and positive power lenses, listed in sequence beginning with the lens closest to the object plane. having a second positive optical power, configured to remain in a fixed position relative to the object plane and to project an image of the object, and comprising three lenses , which comprise negative, positive, and positive power lenses, listed in sequence beginning with the lens closest to the object plane. <EOS>