Mirror Lens Fake
Again I played with my 1.4/55 Revuenon, trying to imitate the bokeh of a mirror lens.
Calculational the "aperture" only absorbs half an f-stop but oddly enough the viewfinder looks much darker. Therefore it's very difficult to focus correctly. Also the camera's lightmeter seems to see the picture much darker and tries to overexposure it. I have no idea about the reason...
The disc is inside the lens, next to the iris aperture.