Here is one of the drawings from Instrument Two. It is a photograph on photographic paper that was held on the picture plane with acrylic plates, so the holes around the edges are from blots that hold the plates (and the photographic paper) to the picture plane. The dark parts are the projection of the white model in the box (projector) and the white parts are the negative of the shadow. below is the positive from this negative (in conventional photographic terms).
The only reason for showing thei image is that it makes it easier to see where the various parts came from, so the projection is now white and the paradoxical shadow is black. The shadow seems to register with the base of the projected model, but is mysteriously smaller, geometrically perhaps appearing to be the object for which the projection is the shadow. You can also see photograms of the plate edges (that hold the paper flat on the picture plane) and some of the registrations cut into the surface of the plates.
Below is a sequence of drawings. The whole sequence can be seen in a picture in the previous post.
The difference between the images is established mostly by folds in the picture plane. As the picture plane adjusts to question the projection, the model int he projector also moves to try and sustain its opinion on the picture plane.