This article offers a theoretical analysis of the 3D cinema experience, paying particular attention to the paradoxical manner in which a further apparatus, medium, or filter – namely 3D glasses – enables what many viewers perceive as a greater level of realism in the cinematic image. That 3D glasses constitute a further apparatus, medium or filter between the image and the viewer ultimately will lead to a more abstract discussion of the differences between ‘solid’ and ‘gaseous’ perception – or, briefly, between seeing objects as solid barriers or as permeable, and of the importance of ‘darkness’ in perception itself. The author’s argument is that darkness, equated here with the extra medium of the 3D glasses, is a key but overlooked aspect of film viewing, something made clear by 3D cinema. Into this argument, he includes analysis of Avatar (James Cameron, 2009), which enacts some of the theoretical arguments that he wishes to make.