Cleaning a Carl Zeiss Sonnar 50mm f1.5

largedrink

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A few days ago I was fortunate to pick up a cheap, filthy Contax IIIA with a beautiful Carl Zeiss Sonnar 50mm f1.5 lens, a lens I have been hoping to acquire for a while. But there's fungus on the rear element adjacent to the aperture blades. I'm looking for advice or instructions on dismantling to clean this. The rest of the glass surfaces appear to be excellent. With current CLA prices I'm reluctant to send this away.

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Note the "Flat Head Screw"- IT IS NOT, this is a guide pin for aligning the barrel in the mount. Do not Touch this. When sliding barrel out of mount, turn lens on side and point this screw down. Be careful of dropping it. It is not screwed in place and will fall out.



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You will need a spanner, Suction Cup OPTIONAL, Blower Optional.

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The Outer Ring holds the Barrel into the Mount.

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Barrel out of mount. The ring in the center is the variable ring, used for stand-off with the barrel in the mount.
 
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The U shaped groove is to align the barrel against the pin.



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It is easiest to remove the rear retaining ring starting with the inner set. As this unscrews, the outer ring comes off with it. Once the outer ring starts out, you can grab it- or use a rubber mat to grab it and finish unscrewing.

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The rear triplet comes out as a module.
 
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Time to reassemble, set the mount with the guide pin as shown.

Set the aperture to F1.5 and position against RIMG0448.jpg

Slowly push in, guide pin pointed down. Rotate until you feel the pin against the groove.

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Move into position, then use the retaining ring you removed first.
 



The U shaped groove is to align the barrel against the pin.





It is easiest to remove the rear retaining ring starting with the inner set. As this unscrews, the outer ring comes off with it. Once the outer ring starts out, you can grab it- or use a rubber mat to grab it and finish unscrewing.



The rear triplet comes out as a module.

Thank you Brian. I have removed the barrel successfully and outer retaining ring, along with the middle variable ring. My inner retaining ring looks a little different to yours. I can use a lens spanner to rotate it, but it doesn't seem to unscrew at all:

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The threads of the innermost barrel will spin once the ring that surrounds it is off. Mike Elek mentioned this. Try using a suction cup on the glass to pull it out.
 
The threads of the innermost barrel will spin once the ring that surrounds it is off. Mike Elek mentioned this. Try using a suction cup on the glass to pull it out.

Success! The suction cup didn't work but I found I could gently work it from side to side with my fingernails on the outside edge and slowly pry it off.

Brian, would it be correct that this lens has hard inner coatings so I should be fairly safe cleaning the inner surfaces?

Also, I see you and Mike Elek mention the variable ring, for precise collimation. I will need to collimate the lens on re-assmbly, is that correct?

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It's back together now and looking great. A couple of spots turned out to be Zeiss bubbles. Ironically now that the rear group is clean, I can see there's some haze behind the front element.... a job for next weekend perhaps. Thank you Brian and Dexdog for the guidance!

Those aperture blades are a work of art:

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Cleaned rear group:

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Lens reassembled and looking superb:

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Well I have in fact encountered an issue. Tightening the final retaining ring also tightens the aperture adjustment so it can't turn anymore.... something is not quite right
 
Barrel out of mount. The ring in the center is the variable ring, used for stand-off with the barrel in the mount.

OK I now understand this part. Obviously I had tightened the middle variable ring as I was working on the lens. Once I loosened it off a little I was able to tighten the retaining ring for the barrel without impacting the aperture ring anymore. Thanks again Sonnar Brian, problem sorted.
 
OK I now understand this part. Obviously I had tightened the middle variable ring as I was working on the lens. Once I loosened it off a little I was able to tighten the retaining ring for the barrel without impacting the aperture ring anymore. Thanks again Sonnar Brian, problem sorted.

Be sure to check the focus after moving the ring used for stand-off in the mount.

I suspect that the barrel might have been slightly off-center to jam the aperture ring- unlike the Carl Zeiss Jena Sonnar, it does not sit against the aperture ring.

The front element- name ring comes off. The front element probably is sitting in a brass fixture. My parts lens is made that way. I've seen a two variations.
 
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Those aperture blades are a work of art:



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Wow! That is beautiful. I don't think I have ever seen a layered aperture blade configuration like that before. Looks like 11 over 11 blades? Might be common but I have never noticed that before.
 
Easiest to get all the lens elements outta the barrel and flood clean with lighter fluid. Getting the aperture blades back in would be a nightmare.
 
I would like to hear some advice about lens cleaning. What is your best practice and what are your recommendations?
  1. What is the recommended way to remove finger prints from front or rear glass? It happens all to often that I touch the glass by accident...
  2. Those old silver Sonnars and Jupiters could look pretty beaten up. Is there a safe way to clean or polish the barrel? Or should one leave it alone to not make more harm?
  3. When I saw the front lens of this old Sonnar 5cm F2 it reminds me of my copy. It looks like it gets a little blind. But I doubt that the cause are cleaning marks. To me it looks like this is some oxidation. Maybe some condensed balsam? Could this be cleaned? I send my copy to get a CLA but I got it back in almost the same condition.
 
I would like to hear some advice about lens cleaning. What is your best practice and what are your recommendations?
  1. What is the recommended way to remove finger prints from front or rear glass? It happens all to often that I touch the glass by accident...
  2. Those old silver Sonnars and Jupiters could look pretty beaten up. Is there a safe way to clean or polish the barrel? Or should one leave it alone to not make more harm?
  3. When I saw the front lens of this old Sonnar 5cm F2 it reminds me of my copy. It looks like it gets a little blind. But I doubt that the cause are cleaning marks. To me it looks like this is some oxidation. Maybe some condensed balsam? Could this be cleaned? I send my copy to get a CLA but I got it back in almost the same condition.

This week has been crazy.

1) I use an Eye-Glass cleaner ammonia/alcohol on a q-tip to apply VERY GENTLY and Tiffen or Lab-Grade Kimtech lens paper to gently wipe off.

2) I use 3M fiber-optic polishing sheets to clean the barrel.

3) That one looks very bad- like abrasion and chemical damage. This lens needs to have the glass polished out by a shop such as Skyllaney.
 
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