Jupiter 12 issues

[stratcat]

I have a Jupiter 12 lenses in Kiev/Contax mount which is completely out of whack. The glass is clean and it mounts easily onto my Kiev 4, but the image it produces is completely out of focus.

As an example, if I look at a focusing screen on the back, point the camera to an object at 2 meters and focus using the rangefinder, the image formed on the focusing screen is 'absolutely' out of focus.

Then, if I try focusing the lens while looking at the screen, it turns out that the image starts coming into focus when turning the lens towards infinity! (yes, with the target at 2 meters from the camera) It never reaches proper focus though.

I'm guessing at some point in it's life it was lubed and cleaned and not properly assembled. I have disassembled it, (following the instructions at Kiev Survival Guide) removed the shim and tried it with the same result. I think the focusing helical was probably no assembled correctly but I'm at a loss at how to assemble it correctly.

Any ideas, pointers, suggestions?

 

[KnipsOmat]

Maybe the infos on Kiev Survival Site can help you?

http://www3.telus.net/public/rpnchbck/Jupiter-12 dismantle.html

 

[wolves3012]

The focussing on a Kiev "expects" the lens to turn 270 degrees from end to end. With the external bayonet (i.e most non-50mm lenses) the lens mount itself is responsible for the correct lens movement, via the pitch of its helical.

Since you can't change that pitch and I think it's not easy to mis-assemble the mount without it being glaringly obvious, I'd suggest that the optics are more likely to be the problem. The rear element is impossible to fit incorrectly but I think it may well be possible to re-fit the front element(s) wrongly. I can't recall the exact optical formula but a plano-convex lens on the front element could be fitted flat-side-out, for instance.

All of the above, of course, assumes the shimming hasn't been messed with badly. However, if it was I'd still expect the lens to form a focussed image, at least for mid-distance subjects, at some point in the focus range, which you're saying it doesn't.

EDIT: +1 on the Kiev Survival site, it's a brilliant resource.

EDIT 2: it's also been known for "serviced" lenses to have an element missing altogether.

 

[stratcat]

Maybe the infos on Kiev Survival Site can help you?

http://www3.telus.net/public/rpnchbck/Jupiter-12 dismantle.html

The focussing on a Kiev "expects" the lens to turn 270 degrees from end to end. With the external bayonet (i.e most non-50mm lenses) the lens mount itself is responsible for the correct lens movement, via the pitch of its helical.

Since you can't change that pitch and I think it's not easy to mis-assemble the mount without it being glaringly obvious, I'd suggest that the optics are more likely to be the problem. The rear element is impossible to fit incorrectly but I think it may well be possible to re-fit the front element(s) wrongly. I can't recall the exact optical formula but a plano-convex lens on the front element could be fitted flat-side-out, for instance.

All of the above, of course, assumes the shimming hasn't been messed with badly. However, if it was I'd still expect the lens to form a focussed image, at least for mid-distance subjects, at some point in the focus range, which you're saying it doesn't.

EDIT: +1 on the Kiev Survival site, it's a brilliant resource.

EDIT 2: it's also been known for "serviced" lenses to have an element missing altogether.

Thanks for your posts. Yes, as I mentioned I used the info on the Kiev Survival Site to disassemble the lens in a, alas futile, effort to correct it's behavior.

I'll check to see if the front element is orientated correctly. How many elements does the Jupiter 12 have? From the info on the Kiev Survival Site and my own experience disassembling the lens I fathom they're three: the massive rear element, and a front and middle one which are screwed together in front of the aperture blades.

 

[farlymac]

You've got a convex single element in front, a cemented pair next, then the aperture, and another cemented pair, then that big honking rear element.

The front pair is convex to the front, concave to the rear. The second pair is flat to the front, and convex to the rear. Hard to reverse the second pair, but the first one may be possible.

It looks like a modified Sonnar design, six elements in four groups.

PF

 

[newspaperguy]

J-12? This might help you:

http://www.sovietcams.com/index.php?1072558845

It's from that site.

Good luck.

 

[farlymac]

That's the diagram I was referencing, Rick. I just couldn't remember where I got it from.

PF

 

[newspaperguy]

We are here to serve. 😀

 

[stratcat]

Thank you very much gentlemen! I was off on vacation for a couple of weeks but now that I'm back the diagram and explanation will certainly be useful in my attempt to get that lens in working order.