US Patent 7088504 Surgical microscope

Binocular luminous fluxes are formed by an objective lens and a pair of relay lenses and go through a splitting optical system, which allows an assistant to observe the same stereoscopic view as the surgeon by using an assistant's binocular eyepiece optical system at a location across from the surgeon via a splitting optical system. Part of at least one of the binocular luminous fluxes is incident on a pupil splitting optical system, forming a binocular luminous flux that has undergone pupil splitting, which allows stereoscopic observation by pupil splitting even when the assistant's binocular eyepiece optical system is rotated to the surgeon's side.