Repairing a Schneider Curtagon 35mm f/4 Lens

The Schneider Curtagon 35mm f/4 seems to be a pretty rare lens. Web searches don't come up with much (any?) information. Everything I was able to find was only about other versions, a "PA" version (tilt-shift) or Retina versions (silver, with DKL mount). On ebay, today, I find a small number of these listed - but in the history ("sold") there are none.
According to a list of Schneider-Kreuznach serial numbers, my lens was made around 1959. It has the M42 mount and a preset aperture with 8 blades. It has a nice weight and feels very well made.

My lens came with a pretty stiff focus, so I thought, I'd give it a try to disassemble and clean it. Although I couldn't find any tutorials, these older German lenses are usually relatively easy to disassemble - so I gave it a try.

Unfortunately, I did not fully succeed: At the end, I was not able to separate the last two pieces to get full access to everything. But I was able to clean and relube most of the lens internals, and able to make a little workaround for the last piece. This gave a huge improvement of the focusing.

I'm starting by removing the nameplate with a rubber tool.

With a lens spanner, I remove the ring that holds the front glass piece.

And I take out the front glass with a suction tool.

This gives access to the ring holding the next glass element.

Now, I can access the aperture from the front.

I continue from the rear side, taking out 3 grub screws that hold the metal ring.

A lens spanner in the outer two holes lets me remove the rear glass.

Now the aperture is accessible from both sides.

Now the front piece can be taken out (I had to wiggle quite a lot!).

This screw is setting the limits to the focus ring.

After loosening this screw, I was able to turn the focus ring until the inner helicoid became free - and further rotating the inner helicoid made it free. Note where exactly it becomes free - and where it exists!

Now, I don't remember what this screw was for (sorry....).

By removing these 3 screws, you can take off the focus ring.

After removing these 3 screws, I was able to remove the back ring.
 

But at this point I was stuck. I have no idea how to separate the inner rotating ring (to which the focus ring is connected) from the rest. Older German lenses (Steinheil, Zeiss Jena, Meyer-Optik) have a second (fine) helicoid for this purpose. But for this lens, it seems that this is not rotating using a helicoid. So, I could not take it off to clean and relube it. But I was able to flush some lighter fluid in between the two pieces, which improved it a lot and it made rotating the focus ring much easier and smoother.

During my attempts to separate the ring, I also tried to remove the helicoid keys. But this did not help, and it was not easy to screw them back on. So I strongly recommend not to try this!!

Due to my failure at this point, I stopped taking pictures of the reassembly of the lens. But since I documented the disassembly in detail, I hope that these pictures are still helpful. 
If you figure out how to separate that last piece, please leave a comment!

In any case, my lens is now in great shape - and it's fun to take pictures with it!

More of my lens repair tutorials can be found here.

Repairing a Steinheil Auto-D-Quinaron 35mm f/2.8 Lens with Exakta Mount

The Steinheil Auto-D-Quinaron f/2.8 35mm is a beautiful wide-angle lens, made in Germany. This piece was made around 1964. It has the legendary "Zebra" look, typical for German lenses of that era, and a fantastic build quality. Optically, it is very close to the Carl Zeiss Jena Flektogon 2.4/35mm (another highly-regarded legendary lens of that era) and it has the same minimum focus distance of only 0.2m.

It's relatively rare, but you can always find a few on eBay (not to be confused with the Macro version which is more expensive). When I got mine, the optics were in great condition, the aperture was ok, but the focus was very stiff. But previously, I worked on the Steinheil 135mm Tele-Quniar, so I expected this to be somehow similar (and it was!).

There is very little information on this lens on the web, and no repair tutorials. But with some experience on other German lenses from that era, I just gave it a try, and I found that it was pretty. I used the following tools:

A lens rubber tool to remove the name plate (one of the first steps), to get access to the front glass element.

Quality screwdrivers

Cotton pads plus lighter fluid (for cleaning the aperture blades) and isopropyl alcohol (I use the 91% version) for cleaning the old grease from the focusing helicoids

The following general rules for lens repairs have worked very well for me.

In every step, I take pictures and/or draw sketches to remember the orientation of the pieces. For things that you see clearly, a sketch may be more helpful, while pictures also document those details to which you did not pay attention.

Immediately after separating a piece, I try to understand how it was connected, and I try to immediately reconnect it again before proceeding further.

Whenever I remove a piece, I clean it and all newly accessible surfaces immediately with cotton pads and isopropyl alcohol, so I have not dirty/oily pieces in my storage container. For small part (screws, springs, ball bearings) I use a storage box with dividers.

I start, removing the back piece which is held by these four screws.

This lever on the back piece is responsible for stopping down the aperture (I recommend to play with the stop-down button and the A/M switch on the back piece to understand the mechanism). In this case, I see that this lever works fine. 

The name ring can be removed with a rubber tool (or alternatively with a lens spanner). 

This lets you remove the front glass element. Be careful, as it may fall out - although in my case it was stuck and hard to extract.

These three screws are hard to access. But they have to be loosened to remove the cylinder. They just have to be loosened a little bit - make sure they don't come out, since it would be a huge pain to reinsert them.

With the front cylinder unscrewed, the second part of the front glass can also be unscrewed. And then, the aperture piece that also holds the rear glass comes out (through the front).

And the rear glass can be unscrewed from the aperture piece.

Now the aperture can be accessed from the front...

...and from the rear side. I did not disassemble the aperture any further and cleaned it in-place.

The aperture looked very clean, and it was very snappy. But still, there was quite some dirt that could be removed with lighter fluid.

At this point, turn the focus ring to a well-defined position - I chose infinity. Then loosen the four screws that hold it in place (again: make sure they don't come out).

After pulling the focus ring off, ...

... I made a mark of the infinity position.

Now is a good time to check (from the back side of the lens), how the inner (black) helicoid is moving when turning the focus ring, and how it is guided by the two helicoid keys. Then slowly and carefully, I turned the messing focus ring counterclockwise (as seen from the front) until the black helicoid exits the helicoid keys and becomes loose. For my lens, this happened after a little more than one full turn of the messing ring (when my infinity mark was close to the "22" of the depth of field scale.

After the black helicoid became loose, I held the messing ring in place and turned the black helicoid approx. 1/3 turn (clockwise, as seen from the front) until it exited the messing ring. It is very important to document where exactly this happened. For my lens, it happened at the place where the slot (which was marked with an "X" that you cannot see in this picture) was at the long scratch of the messing ring (which, I assume, somebody put there for exactly this purpose).

Then, I turned the messing ring back to where it was at infinity when I made the mark (a little more than a full turn clockwise - see above). From there, I first turn it clockwise to see how far it can be turned before it stops (just to have a reference for later). This happens after approx. 1 1/4 turns.
Then I rotate it back to the original infinity position. From there I turn it counterclockwise until it exits - in my case after about 11 1/2 turns.

These are the three helicoid pieces which need to be cleaned.

And this is the "group photo" of all pieces.

After the helicoids are cleaned, I add really small amounts of grease....

...and put everything together, according to my notes how they came out.

With the messing ring at the original infinity position, I add the focus ring.
Please note: If you make a small error in the infinity position, you can later easily recalibrate the infinity focus, since these screws can also be loosened when the whole lens is reassembled.

Cleaning the rear glass (if needed) and screwing it back to the aperture piece...

...and placing this from the front into the lens.

Screwing in the first front glass piece...

... and the front lens (after cleaning, if needed)...

...and adding the name ring.

When adding the back piece, just make sure that the lever sits in the slot.

And that's it! Quickly check that the aperture works (in "A" position it should close when pressing the silver stop-down button; and in the "M" position, the aperture should follow the value set on the aperture ring). Mine does! Very nice to have this beautiful piece back in great shape!

More of my lens repair tutorials can be found here.