A sequence of adjustments to the picture plane as well as to the model in the projector. You can see the shadows of the model on the picture plane. If this is your first view of the blog, the rest of the instrument can be seen in a post further down the page, as can the drawings that result from working with the instrument. The nature and geometry of the folds in the picture plane were developed to provide a range of subtle to developed adjustments within the area covered by the projection lens.
In a later post I will put up some films of the picture plane moving to show its range of folds.