Yep , a Russian Industar 50mm screwed into the front of a Nikon 50 1.8D ,
Makes for a rather interesting result ...
Turns an ordinary 50mm , into a rather serious macro lens ..
The peep hole affect is the small DIA of the aperture , + that the Nikon lens is set back a little , so the distance from the 1.8D to the industar is far enough to make this peep hole affect more pronounced .