A optical system for a viewing instrument with a variable direction of view is disclosed generally comprising shaft, first and second reflectors located at the distal end of the shaft, where the first reflector rotates about an axis angularly offset from the longitudinal axis of the shaft, and an entrance pupil positioned in the optical path created by the reflectors and preceding the reflecting surface of the second reflector. In certain embodiments, the entrance pupil comprises an aperture stop positioned between the first and second reflectors. In some embodiments, the system includes negative and positive lenses located adjacent the entrance and exit faces of the first reflector.
