The optical lantern was the central medium through which Art History professor Willem Vogelsang (1875-1954) taught his students ‘how to see’. As the first ordinarius in Art History in the Netherlands, Vogelsang focused on creating the right educational setting to turn his students into professional art historians. In his lectures the optical lantern and its projected images functioned as a didactic instrument to make his students (visually) understand compositional and stylistic differences and similarities within and between artworks. The lantern allowed Vogelsang to visually open up the world of art history to a whole new generation of art historians.