He put a camera obscura in large holes, which themselves are depicted as vignetting on the photographs.
The Berlin Wall was not used as camera obscura.
I particularly love the use of diptychs to tell the story. Such a simple, but coherent choice with touching results. There's something particularly moving about the ones where the image is just a small circle on the page. I can't quite put my finger on it...
Thanks for sharing, OP.