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Alex
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, May 15, 2005 - 05:09 am: | 
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I succumbed to Ebay yet again and bought a cheap old Zeiss (Jena) Tessar, M42 threaded. 'Very good condition' turned out to be focussing ring jammed solid, so that focussing close just unscrewed the lens right back off the camera, and diaphragm stuck.
The short of it is that I eventually got the lens disassembled (at last, a use for a digital camera as the disassembly proceeded!), the helicoids thoroughly cleaned and lightly re-greased, and everything back and nearly working. The only things not perfect is the diaphragm, and I suspected that some of the grease (there seems a lot of it) from the helicoids had somehow migrated on to the blades. The trouble is, getting in to the blades to clean them is proving difficult. The closest I've got is taking out the rear lens assembly, which has let me lightly clean that side of the blades with naptha and a lint-free tissue. But there are signs of contamination on the front side of the blades too.
However, I can't see how to get the front lens set off. To get this far on what I thought was going to be 'easy' has taken me eight hours, and being this close to getting it all perfect I've got the bit between my teeth, even if the lens did only cost me GBP8.
If you recognise the lens type, it's the Tessar 50/2.8 with 'zebra stripe' rings, and there's a deep recess in the front of the lens mount, though I can't see anything like the threaded rim which held the rear lens assembly in place. Is this front 'recess' held in place by glue or can it be unscrewed?
I'd be grateful for any pointers. |
Tony Duell
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, May 15, 2005 - 05:47 am: |
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If this is the lens I think it is, the name ring unscrews (it's fitted into the filter thread). You need to grip it with a rubber tool.
It's been some time since I took one of these lenses apart (and I worked on the Exakta version), but I seem to remember you can take off the rear section of the mount with the obvious screws on the back. The aperture ring comes off (don't lose the click-stop ball!) next. There is some way of pulling the complete optical barrel from the mount -- I think it's the notched ring on the front, under the name ring, maybe you have to remove some linkages from the back.
The front lens cell should just unscrew out of the optical barrel. You don't need to, but I think the front element is held on by a ring inside the friont of the front cell. |
Alex
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, May 15, 2005 - 01:16 pm: |
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Thank you for the tips, that sounds positive, I shall give it a try. I did manage to get the complete optical barrel out: there's a screwhead on the outside of the optical barrel which runs in a kind of rail or channel fixed to the inside of the 'outer' barrel, so that when turning the focus ring, the optical barrel moves in and out along this rail, instead of rotating on the optical axis. By unscrewing this rail (it's held on by two screws at one end), the optical barrel is now free to rotate and can be rotated right out. That was when I discovered that the helicoids are multi-start, with FOURTEEN start positions to choose from to get it back together again. Guess how many I tried before I found the right one? (The answer is not 'one'!)
I should be able to fashion something out of rubber to get the front ring off. Half the fun of doing this sort of thing is figuring out and making the tools for the job! |
Curt
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, May 16, 2005 - 04:46 am: |
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Hi Alex,
To remove the front ring you might try the rubber tip from a pair of crutches. Was suggested a while ago and since I tried it, I've never found much that works better or easier. Hope this helps. Curt in Canada. |
Tony Duell
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, May 16, 2005 - 12:07 pm: |
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IIRC (and if pressed, I'll pull one of these lenses apart to check) you can remove the optical barrel from the front of the mount _without disturbing the helical threads_. In other words, the focusing mount is left operational when you
remove the optics.
I remember spliting the Exakta version into 3 main units -- the mount (with the auto-stopdown linkanges); the focusing mount ; and the optical barrel. Each part can be worked on separately. |
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