Servicing & Restoring a Carl Zeiss Jena Sonnar 1:2 f=5cm T LTM Collapsible

[mhw]

According to the Sonnar overview, only 2720 of the f/2 collapsible LTM Sonnars were produced. Despite the similar production count to the f/1.5 LTM Sonnar (2850 produced), I have found much less information on the f/2 version. The f/2 version is very scarce on eBay too, unlike the f/1.5 which is almost always available if one is willing to pay. So when one popped up I knew I had to snatch it up. It was in rough condition, with lots of micro scratches, haze, stiff mechanism, and a missing infinity lock tab. The worst being an epoxied-on front filter adapter that took me hours and every technique I can think of to remove.


Eventually I repaired most issues (see iFixit guide). There are a few more lingering annoyances (I categorize this as "restoring" as the lens is already fully functional) that I'd love RFF's input on:

1. What is a good replacement for the infinity lock tab? The one on the early Industar 10 looks very similar.
2. There were no shims between the optical and the focus blocks. I believe shims are typically necessary for fine tuning the distance to the film plane. I haven't tested the lens enough to know if it's absolutely necessary though. Where can I source these shims?
3. The collapsible mechanism is quite loose. Turning the aperture often results in accidentally "unlocking" from the extended position. Once collapsed, the lens barrel wobbles in the slot. Is there a way to improve this? I've heard Canon/Leica collapsible lenses have a felt lining to counter this, perhaps there's a way to apply something similar?
4. I plan to restore the lettering with Testors lacquer paint, but I haven't decided what to do with the brassing due to the front filter adapter. Any suggestions?

Here are some pictures of this lovely little lens after the repairs. It doesn't retract a lot, but the upside is it can be safely collapsed on a digital mirroless adapter.


Mounted on a Leica IIIg

 

[Sonnar Brian]

According to the Sonnar overview, only 2720 of the f/2 collapsible LTM Sonnars were produced. Despite the similar production count to the f/1.5 LTM Sonnar (2850 produced), I have found much less information on the f/2 version. The f/2 version is very scarce on eBay too, unlike the f/1.5 which is almost always available if one is willing to pay. So when one popped up I knew I had to snatch it up. It was in rough condition, with lots of micro scratches, haze, stiff mechanism, and a missing infinity lock tab. The worst being an epoxied-on front filter adapter that took me hours and every technique I can think of to remove.
View attachment 4876003

Eventually I repaired most issues (see iFixit guide). There are a few more lingering annoyances (I categorize this as "restoring" as the lens is already fully functional) that I'd love RFF's input on:

1. What is a good replacement for the infinity lock tab? The one on the early Industar 10 looks very similar.
2. There were no shims between the optical and the focus blocks. I believe shims are typically necessary for fine tuning the distance to the film plane. I haven't tested the lens enough to know if it's absolutely necessary though. Where can I source these shims?
3. The collapsible mechanism is quite loose. Turning the aperture often results in accidentally "unlocking" from the extended position. Once collapsed, the lens barrel wobbles in the slot. Is there a way to improve this? I've heard Canon/Leica collapsible lenses have a felt lining to counter this, perhaps there's a way to apply something similar?
4. I plan to restore the lettering with Testors lacquer paint, but I haven't decided what to do with the brassing due to the front filter adapter. Any suggestions?

Here are some pictures of this lovely little lens after the repairs. It doesn't retract a lot, but the upside is it can be safely collapsed on a digital mirroless adapter.


Mounted on a Leica IIIg

1) The collapsible Industar-22 is probably the most plentiful/cheapest source for the locking tab- if you can get one delivered these days. I will probably use one of mine for a new Nikkor-QC 5cm F3.5 collapsible that I have coming in. I've swapped out parts like this before.
2) Shims are the same as the Jupiter-8. Getting shims made can be expensive. I "Harvested" them from parts lenses. You can also make them from thin wire, paper, and foil.
3) Check the locking tabs- make sure there is come friction on them as you turn. You "could try" bending, but they are brittle.
4) Brassing is not so bad that it will not be covered when you use a 40.5mm filter/hood. I'd try a Black Sharpie around it, and be satisfied.

 

[mhw]

1) The collapsible Industar-22 is probably the most plentiful/cheapest source for the locking tab- if you can get one delivered these days. I will probably use one of mine for a new Nikkor-QC 5cm F3.5 collapsible that I have coming in. I've swapped out parts like this before.
2) Shims are the same as the Jupiter-8. Getting shims made can be expensive. I "Harvested" them from parts lenses. You can also make them from thin wire, paper, and foil.
3) Check the locking tabs- make sure there is come friction on them as you turn. You "could try" bending, but they are brittle.
4) Brassing is not so bad that it will not be covered when you use a 40.5mm filter/hood. I'd try a Black Sharpie around it, and be satisfied.

Thanks for the inputs!

3) I tried applying some high friction compounds on the tabs - anti-slip spray coating, pliobond, etc. It's rather difficult to reach the contact surfaces as the baffle containing the locking tabs won't come off on my copy. The compounds help somewhat but quickly rub off after a few lock/unlocks. The tabs also don't work once the lens is collapsed. Right now if I collapse the lens and point it down, it will fall into the "extended" position. I am thinking if there's a way to apply an equivalent of the felt lining somewhere... again tricky since the stuck baffle prevents a full disassembly of the collapsing mechanism.

 

[Sonnar Brian]

@dexdog may have some ideas. He has this lens.

 

[dexdog]

I have 3 of these lenses, all are a bit loose but they do not slide open when un-locked and pointed down. I have tried to tighten up the small tabs holding the lens mount in compression when extended, but snapped one of the tabs off in the process; this lens had only two of three tabs intact when I got it. As Sonnar Brian mentioned, the tabs are brittle, and tweaking them more than a tiny bit is likely to break them off entirely. I have disassembled these theses lenses in the past, and all had a dark blue felt wiper to add drag/friction to the lens barrel

 

[dexdog]

dark blue felt wiper visible in these pics