Fixin' the Nikkor 50/1.2 Ai-S

[stenrasmussen]

My Nikkor 50/1.2 Ai-S had a damage in the rear lens element so I got hold of another sample which had a fine rear lens cell that I could transfer to my otherwise very good copy.
As thought so done...and my lens has a new rear end.
The drawback with the new addition was the presence of some contamination between the two rear lens elements and this caused some annoying spots to appear in the OOF highlights. To fix this there was no way around but to separate the whole rear lens cell (4 elements). The two front ones came out as a unit leaving the two in the very rear to be separated by unscrewing a fixation ring. A 40.5 mm wide blade (made from a steel spatula) served as the tool for this. Cleaning the glass took a good while and gave me the lesson that Pec Pad tissue is NOT lint free! An hour's work and the lens could be re-assembled and tests show good performance. Will post some before and after shots of the OOF blobs to illustrate the "success" of my operation.
Here's a shot of the lens in pieces:

[Jakov Minić]

Sten is becoming Dr. Lens II!

[Mongo]

Mongo is extremely interested in this.  He also has this lens (or AI version) with a similar very small problem on  the last few rear elements. However, the understanding is that the last few elements are a group which is held together with a type of binding agent that makes the job of separating, cleaning and reassembling them very difficult. For this reason , the exercise has not ever been tried on this lens to date.

you did not mention any binding agent. Is this not true OR perhaps the AI-s version is differently constructed to the AI version ?? either way, very interested to see the resulting test images.

[Bjørn Rørslett]

There is a slight optical difference between the AI and AIS versions of the 50/1.2 Nikkor. The AI has a visibly larger rear element. Possibly a different arrangement of the rear lens cell as well.

[Erik Lund]

Thanks for posting Sten!

However, the understanding is that the last few elements are a group which is held together with a type of binding agent that makes the job of separating, cleaning and reassembling them very difficult. For this reason , the exercise has not ever been tried on this lens to date...

Are you talking about two elements cemented together?

Canada Balsam was used in the old days and the elements can be boiled and will then separate, now it's UV cured glue not possible to take apart.

On a side note; On Noct Nikkor the rear most element is fused into position so basically not possible to separate from the aluminum element housing.

[stenrasmussen]

The rear element on the 50/1.2 is also fused in place and cannot be removed. Access to the front side of that element is from the aperture blade side. I'll dismatle my spare lens and take some photos which illustrate the procedure in more detail.

[Mongo]

thanks Erik - that is exactly the sort of thing Mongo was told. It would seem an infeasible exercise for Mongo t o try and have repaired (which was also the advice he was given). The only real way for this old lens would be to replace the whole rear element group as a one - but again, that is also not feasible unless that part can be found or scavenged.

Mongo is still very keen to see Sten's photos of the dismantling process.

[Hugh_3170]

Sten is becoming Dr. Lens II!

Jakov, I think that it could be a Nordic thing that is associated with the long dark winter nights that are now bearing down on folks in that part of the world. 

(Actually I recall that Sten has written up prior lens projects on the old site, including the repairs to his CV125 that went into self destruct mode inside of itself.)

[Jakov Minić]

Hugh, I don't know what it is but I continually admire their patience, skills, and precision!
The more doctors we have the healthier we will all be

[stenrasmussen]

Here are some pics showing the separation of the rear lens cell. Mind you I didn't have a suitable spanner to separate the two front lens elements. You will note scars and burrs on the metal (aluminium) but this after all a practice lens so bear with my recklessness 
Hope this helps anyway 
First: The entire lens (both cells or, groups)

[stenrasmussen]

The rear lens cell is off.

[stenrasmussen]

Spanner'ing out the two front lenses. They come out one unit here but can be separated with the right tool.
(I kno...I need to modify the spanner used here so that the "teeth" fits in the notches).

[stenrasmussen]

A couple of pics of the two front lenses (fore and aft).

[stenrasmussen]

Out comes the second to last (rear) lens in the 50/1.2 Ai-S. Yup, the tool is home made and works like a charm.
The last image shows the threads for the just unscrewed lens.

[PeterN]

The ability to play with these lenses is a reason alone to buy a few. ;-)
Thanks for sharing.