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Problem with unscrewing the lens ring on the Canon FD 35-70
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Posted: Fri Dec 19, 2025 10:14 pm
Post subject: Problem with unscrewing the lens ring on the Canon FD 35-70
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Posted: Fri Dec 19, 2025 10:14 pm
Post subject: Problem with unscrewing the lens ring on the Canon FD 35-70
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I have a Canon FD 35-70 SSC lens on my table. The problem is that the zoom mechanism rollers are damaged and one lens is dirty. Specifically, it is the last lens of the front optical block. There is fogging inside, and I cannot unscrew the rear ring (applying a minimal amount of acetone to the thread does not help). The manufacturer probably used some kind of “glue” to prevent spontaneous unscrewing. After many years, this agent has glued hard the thread, which makes it difficult to unscrew. At least that's what I suspect.

Can you suggest an effective way to unscrew this ring? I don't want to ruin this fine lens. For now, I consider heating it in the oven to be a last resort.

I am attaching photos of the entire group (without the front lens, which is removed separately, first).

https://www.photrio.com/forum/attachments/dscf6684-jpg.413976/

https://www.photrio.com/forum/attachments/dscf6694-jpg.413977/


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Posted: Fri Dec 19, 2025 10:44 pm
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Posted: Fri Dec 19, 2025 10:44 pm
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Welcome miki11

Other folks will be along shortly with real answers; probably using a drop or two of some sort of solvent on the ring, being especially careful to avoid getting any on the edges of cemented lens elements.


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Posted: Fri Dec 19, 2025 11:22 pm
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Posted: Fri Dec 19, 2025 11:22 pm
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visualopsins wrote:
Welcome miki11

Other folks will be along shortly with real answers; probably using a drop or two of some sort of solvent on the ring, being especially careful to avoid getting any on the edges of cemented lens elements.


There are no cemented lenses in the entire FD 2.8-3.5/35-70mm SSC; therefore I would try to immerse the block for some time in a solvent like acetone. Sometimes it takes a few minutes (or even half an hour) to loosen the elements. I'm pretty sute that this should work - unless the element was factory sealed with an epoxy resin: That would require careful heating indeed.

S


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Posted: Sat Dec 20, 2025 12:43 pm
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Posted: Sat Dec 20, 2025 12:43 pm
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stevemark wrote:
visualopsins wrote:
Welcome miki11

Other folks will be along shortly with real answers; probably using a drop or two of some sort of solvent on the ring, being especially careful to avoid getting any on the edges of cemented lens elements.


There are no cemented lenses in the entire FD 2.8-3.5/35-70mm SSC; therefore I would try to immerse the block for some time in a solvent like acetone. Sometimes it takes a few minutes (or even half an hour) to loosen the elements. I'm pretty sute that this should work - unless the element was factory sealed with an epoxy resin: That would require careful heating indeed.

S


Yes, this zoom lens has 10 lenses in 10 groups. The front block contains 5 separate lenses, and the one that is dirty is the fifth one (counting from the front).

After two days of gently soaking the thread with acetone, I finally managed to unscrew the ring last night. I tried to clean it (with hydrogen peroxide, IPA - 99% isopropyl alcohol, Zeiss optics cleaner), but unfortunately I couldn't remove the artifact. I immersed the entire element in IPA for 10 hours, but that didn't help either. Here is the result after today's inspection.

https://www.photrio.com/forum/attachments/dscf6695-jpg.414018/

What agent can help me remove this “haze” without risking damage to the coatings?


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Posted: Mon Jun 08, 2026 6:41 pm
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Posted: Mon Jun 08, 2026 6:41 pm
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miki11 wrote:

After two days of gently soaking the thread with acetone, I finally managed to unscrew the ring last night. I tried to clean it (with hydrogen peroxide, IPA - 99% isopropyl alcohol, Zeiss optics cleaner), but unfortunately I couldn't remove the artifact. I immersed the entire element in IPA for 10 hours, but that didn't help either. Here is the result after today's inspection.

https://www.photrio.com/forum/attachments/dscf6695-jpg.414018/

What agent can help me remove this “haze” without risking damage to the coatings?


I have encountered this kind of damage on two lenses - on the front lenses of a Mamiya Sekor C 4/210mm and the front lenses of a Pettri 4/200mm. I suspect the surface is etched by some aggessive chemicals either from the lens barrel or from the surroundings. Probably the only way to improve the situation would be re-polishing the lens surface (e. g. with cerium oxide powder).

S


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Posted: Mon Jun 08, 2026 8:25 pm
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Posted: Mon Jun 08, 2026 8:25 pm
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Try pure soap and water.


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Posted: Tue Jun 09, 2026 4:01 pm
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Posted: Tue Jun 09, 2026 4:01 pm
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visualopsins wrote:
Try pure soap and water.


Polishing - or just washing?

I case of the two lenses I mentioned above (Mamiya Sekor C 4/210 and Petri 4/200) the lens surfaces clearly are damaged; simply washing didn't result in any improvement.

Many years ago Zeiss Oberkochen seems to have promoted using cigarette ash for polishing:
https://richardhaw.com/2020/12/13/repair-polishing-glass-part-1/

Not sure whether that's a urban legend, though ...

I haven't tried, but since I have some smoker friends I should aks them for some ash ...

S
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