How can I connect the Nikon el-nikkor 50mm f2.8 enlarging lens to my Canon 5D Mark II? What adapter / reversing ring do I need?
The lens in question is designed for a photographic enlarger which is used during film printing to enlarge the negative onto the photo paper. However, there are places that will, in fact, make adapters one of which is Zörk Film and Phototechnic in Germany. They don't really list the product detail, but if you contact them, they can probably let you know if it is possible. I believe the Multi-Focus System uses enlarger lenses.
For interest, Nikon talks about this lens here: http://www.nikon.com/about/feelnikon/recollections/r15_e/index.htm
I have both the Nikon el-nikkor 50mm f2.8 enlarging lens and a Canon 5D Mark II. I have two ways. 1) Mount the lens on a Canon body cap and use Canon extension tubes to mount the lens. The lens aperture ring is hard to turn, so the mounting to the body cap must be good to avoid the lens twisting off when the aperture is changed. 2) The way I do it is mount a Canon to Pentax screw adapter to the camera, put on Pentax extension tubes (much cheaper than Canon), then, to the extension tubes, I mount the reversed Nikkor with an adapter that I modified. This adapter is part of an old Pentax slide copier that I removed and put in set screws to hold enlarging lenses. But, you could reverse mount the lens to a Pentax body cap, using tape, glue, screws, or the like. ~Bob~