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01-04-2010, 11:44 AM   #1
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C. Z. Jena Biotar 58mm f2 - How does this thing work again?

A few years ago I saw this lens on eBay in an M42 mount. It was cheap and looked interesting so I bought it. It had some fungus but looked cleanable. Changing the aperture totally baffled me and I could never get it fully apart. So I set it aside for later.

Next year I saw an even cheaper copy in an Exacta mount, and found a web site that gave me a clue about disassembly. I figured I would spend ten minutes swapping parts and start using my cool new lens. I don't know why I continue to believe that; lens makers seem to really hate interchangeable parts. So back in the unfinished projects bin for the Biotar(s).

So this weekend I approached the project again. I finally had to destroy one part and one fungus-infected element to finish the swap. I hate it when that happens. I now have the lens put back together and looking cool.





My problem is, I can't remember how the single-ring preset aperture is supposed to work. I think it worked before, after I read some advice here. Does anyone know what I should be doing?

01-04-2010, 11:53 AM   #2
Igilligan
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If it is like my CZ jena tessar you push down on the silver ap ring, spin it to max ap that you want to set... then turn the silver ring to between F2 and your preset ap... the ring on the tessar is spring loaded.


If it is like my helios 44-2 it is not spring loaded so is can be easily set anywhere between F2 and the ap you pre set


PS you polished that up purdy

psps - was it hard taking it apart? Does it require special tools?

My tessar has very stiff focusing, almost spins the lens off the camera. It could us a lube...

Last edited by Igilligan; 01-04-2010 at 11:59 AM.
01-04-2010, 12:33 PM   #3
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The front ring is the aperture control, rotate it to get the desired aperture setting. How many blades in yours? Mine has 20 blades.
01-04-2010, 01:08 PM   #4
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QuoteOriginally posted by Igilligan Quote
If it is like my CZ jena tessar you push down on the silver ap ring, spin it to max ap that you want to set... then turn the silver ring to between F2 and your preset ap... the ring on the tessar is spring loaded.


If it is like my helios 44-2 it is not spring loaded so is can be easily set anywhere between F2 and the ap you pre set...
It's supposed to be like the Tessar, but something is wrong with this mechanism. At least I now can get the aperture open. I probably wasn't going to use f16 a lot.

QuoteQuote:
PS you polished that up purdy

psps - was it hard taking it apart? Does it require special tools?

My tessar has very stiff focusing, almost spins the lens off the camera. It could us a lube...
The polishing is a test. If it ends up with fingerprints oxidized into the surface, I'll try something else. If it stays shiny I can go further.

The lens is partly the easiest lens ever to disassemble, partly impossible. You can access most of the focusing threads very easily by removing the outermost ring on the back. It's the one with large spanner slots just inside the stop-down pin:



It shows the difference between Japanese and German logic. On a Pentax lens, that kind of a ring would hold the rear lens group in. Here, when you remove it, the lens separates into one part containing optics and aperture, and another part containing focus and mount. You can probably use needle-nose pliers in the spanner slots to loosen the ring. Take off the focus part and be careful not to lose a washer that maintains spacing for infinity focus. Focus to minimum distance and the focus helix threads are exposed inside the lens. I tried to add some light focus grease to the threads, and that helped enough to be functional. I should probably clean all the old grease out with a cut-down toothbrush and mineral spirits, then re-lube. The Exacta-mount donor lens focuses almost as easy as an AF lens, so there's room for improvement.

01-04-2010, 03:17 PM   #5
Igilligan
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Thanks for the info... I tried with some needle nose and no luck. May have to try and borrow a spanner wrench from someone.

So do you know what grease I would use for the focus drive threads???
01-04-2010, 06:53 PM   #6
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QuoteOriginally posted by Igilligan Quote
Thanks for the info... I tried with some needle nose and no luck. May have to try and borrow a spanner wrench from someone.

So do you know what grease I would use for the focus drive threads???
I bought some of this stuff:

Grease, Helical #10 (Light) 8ml - Part #: HG-10

It is pretty expensive and very light. It works great for adding some damping feel to an AF lens without ruining AF function. You don't get a huge quantity either, but each lens requires very little. I would at least go with medium for a MF lens. Probably a high-quality lithium grease would work just fine.
01-04-2010, 06:53 PM   #7
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QuoteOriginally posted by xjjohnno Quote
The front ring is the aperture control, rotate it to get the desired aperture setting. How many blades in yours? Mine has 20 blades.
Darn, I only have ten.
01-04-2010, 07:12 PM   #8
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20 blades . . . wow. The ones I have seen have had either 12 or 10. One of these days I'd like to get one of these for my Contax D.

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