A fundamental element of stereoscopic image production is to geometrically analyze the conversion from real space to stereoscopic images by binocular parallax under various shooting and viewing conditions. This paper reports on this analysis, particularly on the setting of the optical axes of 3D cameras, which has received little attention in the past. The parallel camera configuration maintains linearity during the conversion from real space to stereoscopic images. But the toed-in camera configuration often can not maintain linearity during the conversion from real space to stereoscopic images.