DIY Helicoid for Medium Format Enlarger Lenses
There are a many medium format enlarger lenses, which has good optical performance and cost a penny. But the main difficulty of adapting these lenses on a digital camera, in the absence of focuser. I make such focuser from helicoid of the Industar-50. The main feature of lenses for medium-format photographic enlargers in the fact that they have a flange distance approximately 60-70 mm. This allows between the lens and the camera to insert the focuser, using a small helicoid. Also, the second feature of these lenses is that most of them have a mounting thread 39 and 42 mm. Lets go… Twisted lens unit from Industar-50. To this end the reverse side unscrew the nut. Now the helicoid is already possible to use if fixed to it lenses with electrical tape. But I was not satisfied with that option. I want to make a threaded connection. Native filter thread of Industar-50 is on a lens unit and removed together with it. So now you need to do an alternative thread. As such a thread I buy from Ebay step up ring 37-42. 37 mm - the closest size to put a ring in front of the helicoid barrel. 42 mm - standard thread diameter of most enlarger lenses. As it turned out, the thread 37 mm is not included in the front lens barrel, lacks approximately 0.5 mm. They can grind off the barrel with file. Remove the barrel front ring by unscrewing the three screws fix.
Then take a round file and circular movements bore inner diameter of the barrel. I took this for about 10 minutes. Now step up ring perfectly enters the barrel.
Next put the ring back to the helicoid barrel. And paste it back up ring of super glue. Now our helicoid is usable.
Now you can adjust the rear segment with additional M39 or M42 extension rings (through step down ring 39-42). To establish such a helicod on a Nikon camera, you can use the adapter M42-Nikon.