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I got a free copy of the Nikon 200mm f/4 Ai lens.

However the aperture blades are stuck and oily from both sides. I managed to open the lens and clean the blades from both sides with alcohol. I reassembled the lens and its works just fine. However the oils seems to come back over time and the blades are stuck again. I disassembled the lens now for the third time; cleaned the blades and reassembled everything. It always works for a few days but then the oil comes back and glues the aperture blades back together. How can I permanently fix this issue?

Since it was for free I don't want to bring it to a service center and pay a lot of money for it (maybe I would let them fix it if they would fix it for 20$ max). I would prefer to fix the lens on my own. I'm interested in learning how to fix it.

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  • \$\begingroup\$ There's some discussion here. \$\endgroup\$
    – Kahovius
    Dec 7, 2020 at 10:31
  • \$\begingroup\$ I have successfully used (electrical)contact cleaner.on lead shutter.blades of a Manila 80mm f3.8 TLR lens. The “Fix old cameras” YouTube channel had a video suggesting it as a first step because it is easy, might work, and doesn’t make more work if it doesn’t work. \$\endgroup\$
    – Bob Macaroni McStevens
    Dec 7, 2020 at 15:09
  • \$\begingroup\$ You might be able to find a used aperture assembly pretty cheap on eBay (the entire unit). The next time you disassemble the lens, just reassemble with the clean aperture assembly. It's almost totally impossible to get rid of all oil once it has gotten into an aperture assembly. That's one reason why we use grease inside a lens very sparingly, and never use any kind of liquid that could run. It's also why we never apply liquids directly to the outer surface of lenses, but rather place a few drops on a cleaning cloth and then use the cloth on the lens itself. \$\endgroup\$
    – Michael C
    Dec 9, 2020 at 20:53

2 Answers 2

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You need to locate and clean the source of the oil. Most likely, you would have to disassemble the lens, clean out the old grease, and regrease the helicoids.

You should also use a nonpolar solvent (naphtha / mineral spirits) instead of alcohol.

Replacing the aperture assembly is not a viable option.

  • There is no listing for an aperture assembly for this lens on eBay.
  • The aperture assembly on vintage lenses is usually an inseparable part of the optical block or inner barrel.
  • Even if the aperture assembly could be replaced, the best you'd find is a donor lens, which would have the same or worse problems as your current lens. (Otherwise, it would be a replacement lens, not a donor.)
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The old grease will keep running into mechanism. The only way to eliminate the problem is to do a complete CLA. It needs to be flushed and cleaned of all grease, then properly relubed with new grease. Since it is a 200mm it has alot of grease in its long helicoid. If you are not comfortable with a complate disassembly then you should sell it for parts and get another one. A CLA will cost more than buying a good replacement.

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