A stereo comparator configured for use with a stereo endoscope for adjusting and aligning an optical assembly of the stereo endoscope, for example, in connection with the repair of the endoscope. The comparator includes a housing containing a plurality of optical components, namely, a first deflecting component, a second deflecting component, a third deflecting component and a beam splitter. The optical components are arranged so that the first deflecting component deflects a first beam from a right image channel of a stereo endoscope to the beam splitter, the second deflecting component deflects a second beam from a left image channel of the stereo endoscope to the third deflecting component, the third deflecting component deflects the second beam to the beam splitter and the beam splitter combines the first beam with the second beam to form a first combined beam that extends along an optical axis of the stereo endoscope.