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Tak_61
Tinkerer
Username: Tak_61
Post Number: 1
Registered: 09-2011
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, September 24, 2011 - 10:37 am: | 
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Dear all,
it happened to me to have a Biometar 80mm with a beautiful glass (no scratches, no fungus no cleaning marks) but unfortunately the focus ring moves only for 20- 25 degrees from infinty and than it becames hard and does not move any further. The lens was not very expensive so I decided to open it. A clue on a possible cause of the defect is the mark of a strong blow that bend the outer zebrated alluminium barrel
On the other side of the body, if i try to unscrew moving the inner ring with the two "ears" it moves just a bit and then it stucks. I tried to remove the two brakets which hold the two "ears" and doing so the outer ring ( the one with the numbers of meters and feet ) moves but the internal part does not. Maybe there is some retaining screw hidden somewhere? Or the blow coud have deformed the helicoid (I hope not!). Coud somebody be so kind to explain me how to unscrew the helicoid?And/or have an idea on what is that is preventing the focus ring to do its job? Thanks a lot!
(BTW I have posted the same question on other forum) |
Tak_61
Tinkerer
Username: Tak_61
Post Number: 2
Registered: 09-2011
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, September 24, 2011 - 01:54 pm: |
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Glenn
Tinkerer
Username: Glenn
Post Number: 956
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, September 25, 2011 - 07:22 am: |
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If you click on the 'article' box at the top of the page and scroll down to the article by Henry Taber on the 120mm Biometar in the lens repair section, you will find detailed instructions which will also appertain to the 80mm lens - all series Zeiss Jana lenses being of similar construction.
If you then scroll down to the very bottom of the index page you will see the 'External Source' section, clicking on Rick Oleson's excellent 'Tech Notes' will reveal a site that has notes on stripping down Zeiss Jena lenses - again you do not need to be focal length specific, instruction for 120mm or 180mm lenses will be of help.
To aid reassembly you should set the focus ring to infinity, then scribe reference points on all the moving parts that will allow you to count the number of turns required to remove each threaded ring. Generally the procedure is to remove the two removable 'keyways' and then unscrew the outer engraved focus ring, counting the number of turns required to do so with reference to your scribed lines. One does the same for the inner part of the helical, note that after removing the focus ring a stop screw for the inner part of the helical might be revealed and have to be removed first.
If you use a fixed reference point and count rotations during stripdown, reassembly of focus helicals is generally a simple and quick operation. Without this ordered approach, reassembly can become a longwinded trial and error exercise.
The alloy is very soft in these Jana lenses and a strong blow can distort the threaded parts of the helical. Do not try and push out 'dents' on the threaded areas, you will just wreck the threads. First make sure that there is no binding of any unthreaded area - gently working with suitably shaped pieces of hardwood will remove these dents. Then if the helical still binds or is tight, use a fairly abrasive metal cleaner such as 'AutoSolvol' to try and lap out the tight areas. If the damage was not too great this action may free up the focus without further damage - do not allow the undamaged areas of the helical to become coated with the abrasive medium or you will end up will a very loose helical, even after packing with grease. I have used this method to resurrect two otherwise wrecked CZ Jana 180mm/2.8 lenses, the end results being two battle scarred but very useable lenses. |
Tak_61
Tinkerer
Username: Tak_61
Post Number: 3
Registered: 09-2011
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, September 25, 2011 - 10:47 am: |
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thank you, very usefull information, I will let you know about the end of this story... |
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