ZEISS SURGICAL OPERATING MICROSCOPE 0 ZERO DEGREE CO OBSERVATION TUBE f 175 T*. Zeiss Zero Degree Assistant Scope. This assistant scope allows a coaxial view for the assistant without the traditional loss of light from the beam splitter. The unit has its own focusing mechanism. Due to the thickness of the unit the focal distance is fixed at 175mm. This also enhances the depth perception for the primary and assisting surgeon. This co observation tube is ideal for Ophthalmology. Signs of cosmetic usage visible. Please view my other auctions for more ZEISS surgical microscopes and accessories.