Jupiter-12 - Unsharp at any distance

[Kai-san]

I have come into ownership of a LZOS Jupiter-12 in Contax/Kiev mount that is unsharp at any distance. First I thought that it might be a case of the helicoid being out of kilter, but if I have understood the "Kiev Survival Site" correctly this should not be the case if the aperture indicator fits the aperture scale, which it does. Here are two examples:

Focus at infinity, aperture 8.0



Focus on the stone, aperture 8.0


Any suggestions as to the cause of this? The camera works fine with other lenses, so not an issue with the rangefinder.

 

[Sonnar Brian]

The Jupiter-12 uses a Shim for stand-off of the optical block. It's probably off.

But- make sure everything is tight, a loose element can also cause this.
The J-12 uses the same shims as the J-8.

 

[Kai-san]

Thanks Brian, I will open it up and have a look.

 

[wlewisiii]

Yup. My current one is from Brian so I _KNOW_ it's good (aside from the photos 😉) but I've had a number of them over the years and the J-12 is, frankly, one of the easiest lenses to get a good copy of in any lens mount. When it's right, it's a very sweet little lens.

Honestly? A good Jupiter 12 can be the best _FSU_ lens of the bunch. The various sonnars from the old days are a different game but for pure FSU production, they did alright by the J12 and that old school biogon lens.

 

[Kai-san]

So I took the J12 apart, the first thing I noticed was that the grub screw that is supposed to hold the aperture selector assembly in place was missing. It probably has no connection to the problem with this lens, I had to use quite a bit of force to get the aperture selector out. And this is what I observed when it was disassembled:



Not quite what I had expected. The first ring has a thickness of 0,5mm and the second 0,9mm. I do not know how these measures are compared to a J12 or a J8 with only one ring. Maybe I should remove the thinnest?

The helicoid seems to be in the right place:

 

[dexdog]

Maybe I should remove the thinnest?

The helicoid seems to be in the right place:

View attachment 4833281

Removing one of the shims would be a good place to start. Do you have a digital camera to test it?

 

[Kai-san]

I'm 100% analog.............

 

[TenEleven]

In that case you need a piece of ground glass or a plain focusing screen for a SLR, ideally an older one without a heavy fresnel pattern.
Use cello-tape to hold to it the rails of your Kiev/Contax and check focus at infinity with a loupe. A far away high contrast object such as an aerial or radio tower against the sky works very well.

Judging from your images I would say it seems you likely have too many shims (focus is set much too close).

It probably also can't hurt to re-tighten all lens retainers and such. Finger-tight or wrist-tight is enough. No need to force it. Doing so won't improve performance and will just make a worse headache for the next person.

Also seconding that the Jupiter-12 is a great little lens and so far I've had good luck with my M39 copies. That said the copy I had in Contax mount (black LZOS one) was also way off. Since back then it was a 30 dollar lens I just shrugged divided it up for parts.

 

[Brambling]

such a device should help you - schematic diagram of an optical bench

 

[Brambling]

in this case it was made from what was at hand

 

[Kai-san]

I've got everything I need (including a lockable cable release) except light. It's evening here now so I'll have to wait till morning.
Brambling; that looks like a very useful device, did you find ready made extension rings in the correct length or did you have to modify them?

 

[dxq.canada]

You may already have what it takes to collimate ... Mike Elek: Lens collimating

 

[Kai-san]

You may already have what it takes to collimate ... Mike Elek: Lens collimating

I do indeed. I can put a 135mm and the 6x magnifying loupe on my Nikon F3, that should do the trick. I have in fact used this method some years ago on a Franka Solida folder with a fixed lens. Thanks for reminding me!

 

[Brambling]

I've got everything I need (including a lockable cable release) except light. It's evening here now so I'll have to wait till morning.
Brambling; that looks like a very useful device, did you find ready made extension rings in the correct length or did you have to modify them?

These are ordinary extension rings for macro photography M42 and M39.

 

[Brambling]

The peculiarity of this design is the thread pitch of the last ring that rotates - 1 mm, i.e. one full turn - a mismatch of the working segment by 1 mm, half a turn - half a millimeter, a quarter turn - 0.25 mm, etc.

 

[Muggins]

I do indeed. I can put a 135mm and the 6x magnifying loupe on my Nikon F3, that should do the trick. I have in fact used this method some years ago on a Franka Solida folder with a fixed lens. Thanks for reminding me!

That will certainly do the trick, I've done it myself with a 135 on an F3 just by popping the prism off.

 

[Kai-san]

Today I rigged up the collimation set-up, I put the J12 on a Kiev 4; same camera that produced the shots above. I used a ground glass with a mark on the ground surface and made sure the ground surface was facing the lens. Surprise, surprise, with both rings in place the focus is absolutely perfect! With only the thickest ring in place I had to shift the focus on the 135mm Nikkor to halfway between infinity and 20m, with only the thinnest ring in place much worse.
Then I put the J12 on a Contax II with both rings in place, ever so slightly out of focus as if it could have done with perhaps 0,1mm extra shims.
I also tried the method TenEleven suggested, it looks OK though I found it a bit difficult to execute.
I think I need to shoot a test roll with the thinnest ring removed to see what happens.

 

[Brambling]

Today I rigged up the collimation set-up, I put the J12 on a Kiev 4; same camera that produced the shots above. I used a ground glass with a mark on the ground surface and made sure the ground surface was facing the lens. Surprise, surprise, with both rings in place the focus is absolutely perfect! With only the thickest ring in place I had to shift the focus on the 135mm Nikkor to halfway between infinity and 20m, with only the thinnest ring in place much worse.
Then I put the J12 on a Contax II with both rings in place, ever so slightly out of focus as if it could have done with perhaps 0,1mm extra shims.
I also tried the method TenEleven suggested, it looks OK though I found it a bit difficult to execute.
I think I need to shoot a test roll with the thinnest ring removed to see what happens.

Do not forget that Jupiter 12 has a curved image field (a birth defect of the scheme), therefore, if the center is perfectly sharp, the edges may be a little blurry; I personally aimed somewhere 1/4 of the distance from the center, so as not to lose the edges.🤓

 

[Kai-san]

The mark I used was probably 1/3 from the center as this ground glass has a split image and a microraster in the center. When I focus a rangefinder I use the edge of the patch to focus, but the size of the patch varies from camera to camera. I really do not understand what's the issue with this lens. I've used the Kiev 4 after the above shot were made, with a different lens and with excellent results.

 

[dxq.canada]

Hmm, it is possible that after you took the lens apart, then put it back together with both shims ... that this corrected the problem (as the collimation indicates)?