Septum

A septum is a divider in a stereo camera or stereoscope positioned between the two lenses. In a stereo camera the septum separates the two lenses and their image fields. Its primary function is to prevent light intended for one lens from entering the optical path of the other lens.

In a stereoscope the septum is positioned between the observer’s eyes and extends toward the stereoview. Its function is to ensure that each eye sees only the image intended for it. This prevents cross-viewing and enables the brain to combine the two images into a single three-dimensional perception.