Problem with unscrewing the lens ring on the Canon FD 35-70 SSC model

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).

Is this the FD 35-70 f2.8-3.5 SSC lens? I have had mine since 1981 and it is a cracker lens. I saw a reference a while ago where a Canon engineer reckoned that Canon should have put a red line around the lens denoting its superior performance.

Alas, about 4 years ago it developed faults in the zoom mechanism with a rough feeling when turning and when I rock the lens for and aft the is something internal moving a few millimetres. This sounds similar to what you are experiencing. My optics seem ok so one day I may get brave and see what can be done about it. In the meantime I have an FD 35-105 f3.5 zoom as a replacement.

If you want to keep the lens don't whatever you do heat the lens in an oven or anywhere else. If the remaining elements are cemented together with balsam this will almost certainly destroy the cement and your lens will be to all intents and purposes destroyed. You need the correct 'key' which fits into the two slots. The correct tool will be made from very hard metal so it doesn't bend and fits without slipping. I think you have a problem which will be very hard to solve without serious risk of damage.

That lens now will not be worth a lot of money and it may be time to retire it gracefully and look for another.

tokam said:

Is this the FD 35-70 f2.8-3.5 SSC lens? I have had mine since 1981 and it is a cracker lens. I saw a reference a while ago where a Canon engineer reckoned that Canon should have put a red line around the lens denoting its superior performance.

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BMbikerider said:

If you want to keep the lens don't whatever you do heat the lens in an oven or anywhere else. If the remaining elements are cemented together with balsam this will almost certainly destroy the cement and your lens will be to all intents and purposes destroyed. You need the correct 'key' which fits into the two slots. The correct tool will be made from very hard metal so it doesn't bend and fits without slipping. I think you have a problem which will be very hard to solve without serious risk of damage.

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Yes, this is that excellent Canon lens. It is precisely because of its legendary status that I decided to use every means at my disposal to slowly restore it to full functionality. It's not about performance compared to today's designs. I just want to bring it back to life.

The rattling problem is well known; it is caused by worn rollers in the zoom mechanism. I have an idea for how to repair this component. However, first I need to be sure that the optics are in good condition.

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.





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

In short I don't know and any self respecting lens repairer would hesitate to offer advice without seeing the lens first. If they said try this and it made a complete mess of what could be a decent lens would lay them open to being sued for damages. You are going to to have to bite the bullet and employ as professional who may or may not charge for advice. Bear in mid the mark may not be removeable it would possibly be easier to see if you can find another somewhere.

For what it is worth the ridged mark, between the top bright spot and the black spot if that is what you are concerned about, looks like a thumb print, so someone in the past may have had the lens to pieces and not been scrupulously clean when doing so. If it is a thumb print, then the oils from the skin are slightly acidic and may have etched the glass beyond repairing or a repolish and recoat.

Different solvents affect different contaminates. You might try other solvents on the marks. Naphtha, for example. The thumbprint might be made of grease, not skin oil. There are other solvents but they all have serious concerns so you'll need to do your own research and decide your own risk level.

BMbikerider said:

In short I don't know and any self respecting lens repairer would hesitate to offer advice without seeing the lens first. If they said try this and it made a complete mess of what could be a decent lens would lay them open to being sued for damages. You are going to to have to bite the bullet and employ as professional who may or may not charge for advice. Bear in mid the mark may not be removeable it would possibly be easier to see if you can find another somewhere.

For what it is worth the ridged mark, between the top bright spot and the black spot if that is what you are concerned about, looks like a thumb print, so someone in the past may have had the lens to pieces and not been scrupulously clean when doing so. If it is a thumb print, then the oils from the skin are slightly acidic and may have etched the glass beyond repairing or a repolish and recoat.

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Dan Daniel said:

Different solvents affect different contaminates. You might try other solvents on the marks. Naphtha, for example. The thumbprint might be made of grease, not skin oil. There are other solvents but they all have serious concerns so you'll need to do your own research and decide your own risk level.

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I am aware that it is easier to treat a patient when they come to see the doctor in person. These distinctive “combs” resemble parallel lines rather than fingerprints. We have had holidays and family gatherings here over the last few days, but now I will slowly start doing something. First, I will take another close look at this artifact to see if it is located on one surface (or perhaps inside this homogeneous lens). If it turns out to be a surface defect, I will probably try polishing the surface with cerium dioxide (I bought some a few days ago). I know that this could destroy the anti-reflective coatings on the ninth surface in this optical path. However, it is a lens located deep inside, so I think there is a good chance that this treatment will slightly improve the image contrast.

One more thing. I don't know how it is in Anglo-Saxon countries, but here no one is going to sue anyone for an opinion posted on an internet forum. I undertake all such operations at my own risk and I am aware of the possibility of deteriorating light transmission quality after my intervention. Perhaps repair is not possible and it will be necessary to look for another copy or give up on this model.

I managed (in the meantime) to regenerate the elements responsible for the longitudinal and transverse slack in the zoom structure. Now I have to polish the defective surface of the lens (cerium dioxide [IV]).

By the way, I have two questions.

- Is there a service manual available for this model?
- Do the optical paths of the FD version and the newer nFD version consist of identical lenses?

What I mean is, can a lens from an nFD donor lens be used and mounted in an FD lens?

I have finished polishing one side of the lens. The process took around 60–70 minutes and the artefact was difficult to remove. Here is the whole front optical block (with the polished lens). Now I need to finish the mechanical servicing, assemble everything and perform tests.

miki11 said:

I managed (in the meantime) to regenerate the elements responsible for the longitudinal and transverse slack in the zoom structure. Now I have to polish the defective surface of the lens (cerium dioxide [IV]).

By the way, I have two questions.

- Is there a service manual available for this model?
- Do the optical paths of the FD version and the newer nFD version consist of identical lenses?

What I mean is, can a lens from an nFD donor lens be used and mounted in an FD lens?

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Common sense tells me that there will be few if any people on here that can definitively say if any parts can be interchanged. I feel the only people who would be able to tell you are Canon themselves. (but don't hold your breath for a reply!

I think the same way as you