g the input optical paths are preferably parallel to each other and moreover parallel to the optical axis z of the optical system 100 the intermediate optical paths 116 d and 116 g run from each first plane mirror 120 d or 120 g to a second plane mirror 122 d or 122 g according to the principles of optical reflection finally the output optical paths 118 d and 118 g run from the second mirrors 122 d and 122 g and the camera 190 the arrangement of the mirrors shown here is such that the output optical paths are also parallel to each other and parallel to the optical axis z this results from the use of mirrors positioned at 45 u00b0 relative to each optical path so that the light rays along these optical paths are reflected at 90 u00b0 the invention applies however to other positions of the mirrors provided that the multiple reflections project the images of both eyes simultaneously onto the camera 190 moreover the aperture angle of the camera can cause these optical paths to vary slightly a camera with a short focal length for example 8 mm can be used to provide significant compactness in this case when the optical system is designed a fine adjustment is made to the focussing of the camera 190 in order to take into account errors in the positioning of the mirrors in the optical system it should be noted that the variations due to the.