J12 Adjustment

[Brother Joe]

I recently acquired a Jupiter 12 and haven't had much time to shoot with it.

I ran a roll through it and then decided I wanted a yellow filter on it. I had the filter on, and I swear the aperture ring moved inside the body (as in, I was at either 22 or 2.8 and it moved as a unit).

I ran another roll through it and developed both today to find that it is horribly out of focus...

I ran a quick test roll through it with a placard with the lens/body I was using and discovered that the 2 I26M's I have are fine, yet the J12 is out of focus.

I've got 2 FED bodies, and have run a roll through it doing the same test, but, haven't developed it, but, I suspect I'll find the same.

So, onto my question: has anyone got any instructions or a link to how you adjust one of these?

I verified that the rear element hadn't become unthreaded, as I spotted that as an issue in other postings.

I'm not very clear on how the lens is put together and what might be wrong, so, I need a bit of smacking with a cluestick.

Thanks
J

 

[Sonnar Brian]

I've done this with the Contax/Kiev mount version.
The rear element unscrews to come off, then the front optic can be unscrewed with a hollow rubber grommet or spanner. You will see the shim under the front module. It's fairly small.

The lens should not be too far off, it is a wide-angle lens. If it is way off, something else is probably wrong. Other problems besides the shim: It could have an incorrectly reassembled helical, or could be missing an element. I've seen both happen.

 

[Brother Joe]

I've done this with the Contax/Kiev mount version.
The rear element unscrews to come off, then the front optic can be unscrewed with a hollow rubber grommet or spanner. You will see the shim under the front module. It's fairly small.

The lens should not be too far off, it is a wide-angle lens. If it is way off, something else is probably wrong. Other problems besides the shim: It could have an incorrectly reassembled helical, or could be missing an element. I've seen both happen.

Ok; I think I'm where you're talking. I now have 4 pieces.

Rear element; "casing", since I don't know what it's called, an aluminum shim that sits over the front element, and, the front element.

If I look at the aperture/front element, I see there is a single small set-screw that seems to hold the element and the aperture adjustment/hood together. I note that that isn't flush back, it's actually out (away from the camera body, if one were present).

This doesn't seem to have any function on focus/lens alignment, but i suppose it should be out where the casing doesn't make it too difficult to reach the aperture adjustment.

So, anyway; what is the end result here: did you wish me to ensure the shim was in place, and then, should I ensure that the front and rear elements are seated firmly in the lens body/casing?

*flash*

I also discovered that once the front and rear elements are rejoined in the body, they will actually thread in/out of the body some distance. I'm wondering how this should go. Ultimately when unthreading the rear-element, the whole front/rear element will spin, until finally you hit the end of the threads of the front element coming back through the body; then I can unthread the rear element... Does this make any sense? I'm not quite certain how to describe it!

At anyrate; I figure one should tighten the rear element to the front, then, thread the two back into the lens body (clockwise) until snug?

Thanks Brian 🙂

J

 

[Sonnar Brian]

The shim controls the distance to the film plane when the front and rear are back together. It's that shim's thickness that is usually the issue. It has to be the correct thickness for the focus to agree with the RF. But- Ive seen lenses with missing elements, and some helicals that were incorrectly assembled.

Post some pictures with the lens if possible.

 

[Brother Joe]

The shim controls the distance to the film plane when the front and rear are back together. It's that shim's thickness that is usually the issue. It has to be the correct thickness for the focus to agree with the RF. But- Ive seen lenses with missing elements, and some helicals that were incorrectly assembled.

Post some pictures with the lens if possible.

Will do; I have a partial roll that I shot with it and I *think* half of it is in focus. I put the lens back together making sure everything was snug and will take a couple more shots to see if the problem was the elements being loose or shifted in the lens body.

I don't think I got a bum lens!

I'll report back.

J

 

[Brother Joe]

Brian,
I developed a roll last evening that seems better. I suspect the front and rear elements had come loose from the housing and had moved forward. It's still not perfect, but, this morning before I left I did a couple of tests at 1 and 2 meters where I set the distance scale and then shot, then I peered through the VF and adjusted that to be "focus".
I figure I'll shoot up the rest of the roll today and have another look.

I stumbled across your J8 write-up at pentax-manuals and gave that a read-through. I hope I don't need anything as drastic as had to be done there, and, if anything I'll fuss with the shimming.

I'll post some shots with the lens with my written distance tests and see what everyone thinks. I've got 2 bodies to test with as well. I started to suspect that initially the lens was out of wack, but, there also may be some VF calibration to be done so thats why I reverted back to doing distance scale.

J

 

[Brother Joe]

OK: this gallery has some photos with the lens. Excuse the under exposed/developed nature 🙂. The one problem I don't necessarily need is a lens that's out of adjustment!

http://www.rangefinderforum.com/photopost/showgallery.php?cat=8107

I was really disappointed to find that it's still not cool. Lens did come from an RFF member, and, I don't believe I was sent a bum lens; I suspect it was loosely OK when I got it, and then having it come apart means that it's unhappy.

J

 

[Brother Joe]

Aha! Success.

/me gets out the crop and wails on that horse!

I shall be posting photos of how a J12 (or, rather, my J12) should look when it's working correctly.

I had 2 problems;

1) When I disassembled the unit; I reassembled it incorrectly, placing the shim between the rear element and the body. It should go between the front element and the body.
2) When I initially re-tightened the front/rear elements, I ran them in the wrong direction.

On my J12, when the elements are properly tightened together, and then tightened in the main body, the aperture ring is nearly flush with the focusing ring/hood of the lens body (this makes it tough to change the aperture, unless one has a filter threaded in).

This means that the front/rear lenses are threaded into the body until the rear element is as far back as it can go. I think Brian says in one of his Jupiter documents that it's difficult to put into words how something goes, this is one of those times 🙂.

Thanks for listening.

Joe

 

[Nikon Bob]

I am glad you got your J12 sorted out. I could not believe that a J12 was as bad as the photos you posted in a link indicated. Just used mine on a Canon P and was pleased with the results even at 2.8 and close. I am sure you will enjoy it.

Bob

 

[Sonnar Brian]

I'm going to have to take mine apart just to document. Once Summer is over, and things turn cold, out come the project lenses.

 

[Brother Joe]

Not that you don't know this 🙂, but, it wasn't quite as complicated as I initially expected. When you don't know how things are constructed and you need to work on them you're never certain what should move and what shouldn't, and how much force to apply where!

I had the rear element off once when things first went awry, but I had little clue just what I should turn next.

The focus is smooth, so, I didn't see any reason to delve deeper and CLA it.

I have an I26m that has a "stiff spot" as you go towards infinity. It feels like as the focus is moving, you hit a set or grub screw in the mechanism and the same drag continues to infinity. How difficult are these to open up?

J

 

[wolves3012]

I have an I26m that has a "stiff spot" as you go towards infinity. It feels like as the focus is moving, you hit a set or grub screw in the mechanism and the same drag continues to infinity. How difficult are these to open up?

J

A lot easier than a J-12 I'd say. I've done half a dozen I-26/I-61s, they always seem to need it (they're the same construction). It's not difficult. See this site:
http://www.pentax-manuals.com/repairs.htm

 

[Brother Joe]

Are there different models of the I26, like with a J8? Both of mine have the focusing tab on them. Looking at the J8 CLA on that site: some variants are more difficult to service than others.

The action of this lens is really smooth, except for the "catch". I wonder if something isn't in there and hopefully it'll be an easy fix.

J

 

[Sonnar Brian]

I've only seen one version of the I26, but have only owned 2. In both cases the optics were bad, and the mount was used for experiments.

 

[rxmd]

There are different I-26 versions as well, with or without focusing tabs, with knurled or ribbed focusing rings etc. I have two different ones. On the web, see for example these: