This picture is about the twin-lens reflex cameras which represent a technical improvement of photography throughout history. These cameras are for better framing what would actually appear in the photograph. However much like stereoscopic vision, a twin-lens camera will show two images distorted due to perspective projection. Only one of them is printed on film. As humans, both our eyes use this information to extract tridimensional characteristics. But it is a problem with the camera which won't give exactly what the photographer sees.