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Sigma 70-210 f/2.8 (Minolta MD) disassembly

oldglass View Drop Down

Joined: 17 May 2020
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Post Options Post Options   Quote oldglass Quote  Post ReplyReply Direct Link To This Post Topic: Sigma 70-210 f/2.8 (Minolta MD) disassembly
    Posted: 17 May 2020 at 18:41

A while ago I gambled on an old manual focus Sigma 70-210 f/2.8 APO for cheap and unfortunately it has fungus growth that gives it an ugly haze. There's also a few individual spots as well but I'm assuming they don't impact the IQ as much. The haze impacts the contrast quite a bit (I assume so anyway, as I have a very cheap Sigma 70-210 f/4-5.6 that looks significantly better than the f/2.8 even stopped way down) so I'd like to try and clean it up.

I've managed to disassemble the lens to a point but I'm stuck and can't figure out how to proceed further. I've got pictures to show where I'm at.

As you can see, compared to the full lens (allphotolenses image) the mount, shell that holds the tripod collar and shell that holds the zoom and focus rings have all come off successfully. That inner column holds the zooming elements.

I found this thread detailing someone's similar plight with the auto focus version of this lens. Some of the details there sound similar but I'm not sure what they meant by "zoom ring mechamism". I've got the zoom ring off, but if they meant the whole assembly containing the moving zoom elements then they're past what I got to. Of course, I'm assuming the construction of the auto focus versions are roughly similar to the manual ones, which could be completely wrong.

You can see there are some screws left on the zoom mechamism but they're extremely shallow flat-head... heads and I don't think I have a bit that can grab them properly. I do wonder though if at this point there's a way to remove the entire zoom group in one go and gain access to the front of the zoom group and to the focusing elements, and hopefully to the glass surface(s) containing the worst fungus.

I'm not sure how to translate Gubbe's story about twisting and turning and eventually freeing a threaded ring into my lens. The only 'ring' I can see is the one creating the lip you see at the rear end of the front shell. Handling the lens and twisting and turning I can feel some kind of play but no idea if that's something almost unscrewing or just regular mechanical play.

I know this isn't a Sigma-specific board and what I have here is pretty obscure by 2020 standards, but there's clearly some expertise on these forums so hopefully someone can help me out.

Thanks in advance.

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neilt3 View Drop Down
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Joined: 13 September 2010
Country: United Kingdom
Location: Manchester.U.K
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Post Options Post Options   Quote neilt3 Quote  Post ReplyReply Direct Link To This Post Posted: 17 May 2020 at 22:20
Just be aware that the recent thread on here that you linked to resulted in the distruction if the lens , not a repair !
see my photostream on flickr;
C & C welcome.
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beeton View Drop Down

Joined: 02 December 2014
Country: Canada
Location: Beeton
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Post Options Post Options   Quote beeton Quote  Post ReplyReply Direct Link To This Post Posted: 29 May 2020 at 17:32
The image seems to be of the underside of the screw. So, you would have to go in from the top. I don't have this lens and have never held one.I believe, with the Sigma af version, the top, shiny part of the tube unscrews. That may allow for the front assembly to slide off and give access to the insides.
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