DIY Helicoid for Medium Format Enlarger Lenses
There are many medium format enlarger lenses, which have good optical performance and cost a penny. But the main difficulty of adapting these lenses on a digital camera, in the absence of a focuser. I make such a focuser from the helicoid of the Industar-50. The main feature of lenses for medium-format photographic enlargers is that they have a flange distance of approximately 60-70 mm. This allows 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. Let's go… Twisted lens unit from Industar-50. To this end, the reverse side unscrews the nut. Now the helicoid is already possible to use if fixed to its lenses with electrical tape. But I was not satisfied with that option. I want to make a threaded connection. The 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 the file. Remove the barrel front ring by unscrewing the three screws fix.
Then take a round file, and circular movements bore the 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 the ring of super glue. Now our helicoid is usable.
Now you can adjust the rear segment with additional M39 or M42 extension rings (through the step-down ring 39-42). To establish such a helicoid on a Nikon camera, you can use the adapter M42-Nikon.