Thanks to a recent YouTube video by John Gravett I knew how to take the front element out of a Helios 44-2 lens and reverse it. Here's the result, complete with a little bit of added texture.
This is a Nikon full frame body, with a short extension tube then a reversed Helios 44-2 adapted to Nikon F mount. This lens is very manual and doesn't focus to infinity any more. The extension tube allows you to get closer to the subject and fill the frame. I focussed by rocking back and forth.
Original straight out of camera image in the extra.