After seeing this post on flickr I decided to try it on my M42 mount Pentacon. Everything went smoothly but after mounting the lens on my Nikon D5100 infinity focus still wasn’t achieved. I tried to turn the focus ring more but it was at it’s maximum and so I forced it a little and mounted on the camera. Still no infinity focus and now the aperture ring didn’t work anymore. So I loosened the screw again and turned it back until the aperture ring worked nicely and then tightened the screws back. I have no problem with the rear element of the lens hitting the mirror but I had no infinity focus. Then I turned all the way to F16 and voila Infinity focus. Apparently when the lens is opened it won’t focus for infinity.
Hope this helps.