Repairing a Carl Zeiss Jena Triotar 135mm f/4 lens

In this post, I give detailed instructions how to disassemble, clean, and re-lube the early, slim version of the Carl Zeiss Jena Triotar 135mm f/4 lens.

The Carl Zeiss Jena Triotar 135mm f/4 lens was created in 1938 for 35mm SLR cameras. Production was stopped in 1958 after Zeiss rediscovered the Sonnar in 1957. It is a triplet (3 elements in 3 groups) and it was made with Exakta and M42 mounts. The earlier version (top) is slimmer while the later more common version (bottom) with preset aperture is much wider. Both have 15 aperture blades.

Most pieces that you can find these days have in common that their focus and aperture rings are very stiff. In the piece that I got, the focus was completely stuck, and when trying to turn the focus ring, you could hear the grub screws scratch over the metal (ouch!).

Please read all of the following before you start, to get an overview of what tools are needed during the procedure. Also, you may find that you could do things in a different order. I have the habit of cleaning every single piece of a lens - every screw and every surface. I'm using paper towels, cotton swabs and 90% isopropyl alcohol and/or Zippo lighter fluid.

I start with loosening the three grub screws on the focus ring (1.), which then slides to the front. Be very careful that these don't come out! They can easily get lost (that's why I worked on rubber mat) and it's a pain to insert them again (believe me, it happened twice to me). This gives access to the two "guide screws" (2.) which "guide" the focusing helicoid. If you unscrew those, you can remove the helicoid. Be very careful to check and note where it exits, since there are 12 entry points and only one will give you the correct focus range (and reach to infinity).

Now you can also remove the focus ring. In the back piece, you can see a black ring which is screwed to the focus ring. This defines the limits within which the focus ring can be rotated.

By removing this screw, that ring becomes loose ...

... and one can unscrew the focusing helicoid (remember the positions of the rings before unscrewing the black ring, and to count the number of turns before the fine helicoid exists - make sketches and take photos!). Now the fine helicoid can be cleaned.

I continue with the front piece.

The front element can be easily unscrewed - then the aperture ring can be removed after loosening (not removing!) the three grub screws (as you can see in the picture, mine is missing one, but that's good enough to hold it).

With the aperture ring removed, you have access to this screw (3.).

When this is removed, the black ring (which controls the aperture) can be unscrewed.

Here you can clearly see that it was the old sticky grease which caused the aperture ring to move so poorly. 

I made a very thin scratch on the black metal, to note the position where the red arrow was pointing at. After removing the grub screws (4.) the silver ring can be removed and you get full access to the helicoid.

From the front you also get access to the aperture blades. Surprisingly, mine had no traces of oil (yes, they look dirty in this picture, but there is nothing that comes off with lighter fluid on a cotton swab).

Now the lens is fully disassembled (... at least as far as I plan to disassemble it...).

Now, I make sure to clean everything as good as possible, especially the helicoids. And then, I do all steps in reverse order.

I place the wide silver ring over the front piece, align with the scratch that I made, and tighten the grub screws (one can later still re-align this, if needed).

I put a really tiny amount of helicoid grease on the (cleaned!!) threads - only three small drops at three different places, separated by 120 degrees. I use as little as possible - any excess makes it harder and harder to turn. At the end, the screw is inserted again...

... and the aperture ring is fixed with its grub screws.

And I check that the full open aperture corresponds to the "4" setting. 

Now, I work on the focusing helicoids.

Again: I use only tiny amounts of grease. First, on the fine helicoid, which gets inserted (with the black ring in-between).

In the right position, I fix the screw that holds the black limit-setting ring.

I put a (small!) amount of grease into the coarse helicoid, place the focus ring in between...

... and insert the helicoid exactly where I noted where it came out. In the final position, the slits have to align with the holes for the guiding screws.

When this is achieved, I insert the guiding screws....

... slide the focus ring back, and fix it with the three grub screws.

Now, the lens is ready!

I still have to clean the front element - but that's another story.

Complication

The above description should usually work. In my case, however, there was a really unexpected problem in the very last steps: I was not able to insert the "guide screws". 

So, I took the focusing helicoid apart, and I noticed that their flat (unthreaded) end, which is supposed to fit into the helicoids slits was too wide - and didn't fit.

It's also suspicious that both screws look slightly different...

First, I was a little hesitant, but then I filed the ends of the screws down until they matched the slits.

Of course, I had to be careful not to harm the threads! But it worked!


More of my lens repair tutorials can be found here.