In order to allow the assistant also to make an observation of the same region of the object as by the surgical operator in the form of a normal and clear stereoscopic image, and to enable the size of the barrel as well as the price to be about the same as that of an ordinary surgical microscope having...http://www.google.com.hk/patents/US4763968?utm_source=gb-gplus-share專利 US4763968 - Surgical microscope
