EL-Nikkor 50mm f2.8 on focusing helicoid. Click to see larger.
Many people, including yours truly, have been trying to make this lens focus to infinity on DSLRs, but without much luck, until the NEX, of course. After acquiring the focusing helicoid, I find so many uses for it. All those lenses that could not be used before suddenly are given a new life!
I mounted the EL-Nikkor 50mm f2.8 enlarging lens on the 17-32mm helicoid, through a 52mm filter ring. Works perfectly, and actually focuses past infinity. In case you are not aware, the EL-50mm f2.8 is a very highly regarded lens. Truly flat field with excellent sharpness from corner to corner. The best feature, of course, is its very fast maximum aperture of f2.8. Don't laugh, f2.8 is very bright for enlarging lenses. Most of them have maximum apertures of f4 to f5.6 or even smaller. You can actually use this lens as a normal 50mm lens, except it's sharper than most 50mm lenses, especially at close range. If you have an NEX camera and like to tinker with enlarging lenses, grab one from eBay. It's still El Cheapo in price, but what you get in return in optical quality is unequaled.
Double Happiness -- NEX-5 & EL-Nikkor 50mm f2.8 @ F2.8. Click to see larger.