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Cooke 6 1/2" f2.5 lens from RB series C

 
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disemjg



Joined: 10 Jan 2002
Posts: 469
Location: Washington, DC

PostPosted: Sat Nov 14, 2009 1:02 am    Post subject: Cooke 6 1/2" f2.5 lens from RB series C Reply with quote

I just acquired a very nice RB series C camera from the fabled online auction forum.


While I was hoping for a problem free lens, it was not to be. These are by all accounts almost never found without issues related to the lightweight (magnesium) lens barrel. On my lens, the linkage between the diaphragm and its adjusting ring is not working, and while annoying that is tolerable. Less so is that the rear cell of the lens will not fit the back of the barrel (the barrel is also frozen in the flange, essentially locking the entire thing into the body). Close examination shows that the threads of the rear cell (brass) are too small by about .009" to engage the threads of the rear of the barrel. While I cannot inspect the rear threads closely because of the previously mentioned fact that the barrel is stuck on the body, my guess is that the magnesium threads eroded and can no longer engage the rear cell. While I have some ideas for what would be drastic solutions, for the present time the rear cell is stowed in the pack back on the camera. The front cell fits correctly and you cannot tell that the lens is not all there to look at the camera.

So, for anyone else out there with one of these lenses, have you encountered such a problem with the threads at the back of the barrel? I suspect that the brass of the rear cell may have something to do with the problem, as the front cell threads are good, and the front cell cup is made of magnesium.

I have also applied a bit of penetrating oil between the barrel and the flange, in the faint hope of getting the barrel loose. I have heard all too much about how fragile these are, though, and will not try very hard to fix it. My understanding is that the surfaces weld themselves together and any attempts to separate them will break things. Any tips about this would also be appreciated.

John
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glennfromwy



Joined: 29 Nov 2001
Posts: 903
Location: S.W. Wyoming

PostPosted: Sat Nov 14, 2009 3:21 am    Post subject: Reply with quote

I've dealt with similar situations and I'm sorry to say It's probably a lost cause. The best suggestion I have is to leave everything as is and mix up a gob of JB Weld and glue the rear cell into the barrel. You can shoot it wide open for some really interesting effects at portrait distance while you search for a functioning lens. I hate to be negative but I've never succeeded in getting a corroded lens like this apart in one piece.
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Glenn

"Wyoming - Where everybody is somebody else's weirdo"
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45PSS



Joined: 28 Sep 2001
Posts: 3208
Location: Mid Peninsula, Ca.

PostPosted: Sat Nov 14, 2009 4:45 am    Post subject: Reply with quote

I have had very good results with Liquid Wrench Super Penetrant on corroded parts. It may take a few days to work.
Product Info
I do not know if it will work on this problem but if the penetrating oil does not it may be worth a try.
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The best camera ever made is the one that YOU enjoy using and produces the image quality that satifies YOU.
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semihemi



Joined: 25 Oct 2003
Posts: 85
Location: Boston, MA

PostPosted: Tue Nov 17, 2009 4:00 am    Post subject: Reply with quote

Ouch, sorry to hear the outcome. I had my eye on that camera all the way through the auction - it was tempting indeed! Please keep us posted if you have any success in getting it back into a state of health. How are the elements themselves? One of the auction photos made it look as if the glass was funky. Was that just an illusion?

Thanks,
Semi
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