|Posted: Sun Apr 16, 2017 9:45 pm Post subject: Carl Zeiss Pancolar 50mm f/1.8 conversion to Nikon F
I'd like to share with you a hobby project I was working on for a few weekends. I picked up a Carl Zeiss Jena Pancolar 50mm f/1.8 with M42 mount on ebay for cheap, and decided to fabricate it a new shorter back for Nikon F. With an adapter, it focused barely 2 meters far, so the goal was to give it infinity focus. Under self-imposed rules, I could only swap out parts (so the entire modification is reversible) and I was not allowed to modify anything from the original parts unless absolutely necessary.
The new back was made from three components. Two were custom made from an aluminium alloy (6061-T6), turned to shape on the lathe with a few things done by hand, such as filing a dent for the aperture lock. The third part started as an M42 to Nikon F mount converter, since I wasn't confident in my ability to make a proper Nikon F mount just yet (and didn't feel I have the right tools to do so), and then also turned into shape on the lathe to make it fit with the other two parts. The three parts are glued together using Loctite, and there is also a locking screw for additional mechanical security of the fit between the lens mount and the lens body.
Measurement was a trial and error process, at some point I was shaving off just 0.01mm at a time and re-testing, worried about losing structural soundness since one of the walls is just 0.6mm thick. The end result is fine though, the lens focuses to infinity (or at least close enough I can't tell), and the mechanical build is overall good in no small part thanks to the chosen aluminium alloy. There are some minor quirks, and I've got them reflected in a CAD file alongside the measurements if I decide to do another version. Probably the least successful part of all this was my attempt at chemical blackening of the aluminium. The colour faded out into more grey than deep black I hoped for, as you can see in the photo. I think I know where I went wrong though. :)
Unfortunately I also had to remove some material from the original lens after all, because a part was sticking out enough to hit the camera mirror. However, it was a fairly straightforward surgery with a hand file with no real negative impact. The original back is undamaged, and can be mounted back to turn it into an M42 lens again.
All this was a great learning experience! I hope you'll find it interesting too.