Nightmare first generation Sonnar 50/1.5 repair.
So, I finally worked up the nerve to attack a Nickel and Black Sonnar 50/1.5 I have had lying around for a year now. There had been several failed attempts (by me) to get the rear mount off - to no avail. In the meantime I found a dead 50/2 also Nickel and Black Sonnar of the same generation. The glass was completely ruined and not salvageable. Due to the different optical diameters a transplant from a collapsible or J8 was out.
The Nickel 50/1.5 Sonnar had its rear mount stuck in a half unscrewed position. Most likely from a previous persons repair attempt. As you can see below it had been unscrewed quite far but not enough to free it.
Of course in a state like that it would not reach infinity even on a Nikon body. It was a permanent macro-lens.
I already had tried my entire repertoire of tricks: put it into solvent for a week, put it in an oven, hit it with a blow-torch, put it in a dummy mount and try to wrench it free, etc etc. No dice. The mount would not move. A transplant into a Jupiter-3 mount was out of the question for the same reason the 50/2 could not be saved. Different optical fixtures.
Anyhow, now with the dead 50/2 in my parts box as well I had a plan, but lacked the nerve to do it:
Sever the rear mount of the Black f/1.5 Sonnar and transplant the nice condition mount of the f/2 Sonnar.
However I was very wary because I knew that if I cut too deep I'd irreversibly damage the lens barrel of the f/1.5 Sonnar making it unusable. As a first step I used needle nose pliers and just brutally broke off as many parts of the mount as I could so that there would be less material to saw through and less likelihood of something to go wrong. Then I took a small hand-saw and got sawing millimeter by millimeter. Then I made another incision and carefully pried the piece away leaving the mount in a C shape which could then be taken off the lens.
What I found inside confirmed why I had such trouble. The set screw that holds the mount had broken in half and the previous ... dare I say butcher... hadn't noticed this and had tried to wrench the mount off with great force - grinding the set screw into a fine paste. Somehow the female helical survived this ordeal(!). The picture below is a "re-enactment" of what I found with the exception that the male threads were full of ground up set-screw parts. No wonder it would not move.
I also re-applied fresh lens blacking since the old one had flaked all over the aperture and become one with the oil on the aperture. Everything was cleaned as the debris from the wrecked set-screw had gotten into every last bit of the lens over time.
Finally the lens is back together now and focuses right and works beautifully once again. I sadly didn't take too many pictures as you probably can guess this was a white-knuckle experience for me. Of course due to the female helical start being different on this mount the aperture index is offset so that it's on the top with the camera set to ~15 feet. A small price to pay. I guess I could eventually re-index the aperture but that would still leave an unsightly hole where the old index was on an now otherwise beautiful lens.
No wonder Zeiss moved on quickly from this design.
