Jupiter-6-2 - alignment of aperture markings?

[BigMackCam]

I just picked up a really nice Jupiter-6-2 2.8/180 in lovely optical, mechanical and cosmetic condition. I'm really pleased with it, but there is one minor niggle...

The aperture index dot at the front of the lens, as well as the preset and stop-down rings, are rotated about 150 degrees from where they should be - ie. the dot doesn't align with the red focus index mark on the top of the lens, and isn't visible when looking down at the top of the camera (does that make sense?).

This isn't affecting use. Everything works as it should, and it's really no inconvenience, but for cosmetic reasons I'd like to re-align the aperture dot, preset and stop-down rings.

Can anyone advise how to do this? I have a little experience in basic servicing of prime lenses (Industar-50 & 50-2, Helios 44M and 44M-4, and Jupiter-11A), but I wouldn't call myself a pro by any means. If the procedure is particularly difficult or risky, I'll leave it be. Otherwise, if it's straightforward enough, I'd like to do it.

Many thanks in advance!

[tomasg]

I just did a full CLA of my Jupiter 6 a few days ago, if i understand the problem correctly try to do this: hold the front and the back of the lens and try to unscrew the two parts, turning counter clock wise. The lens can be separated into 2 blocks (the optical and the focusing) this way, like the Helios 40 for example. But a warning, if you can t untighten it with reasonable force stop, there are other ways to open separate these two parts. Once this is done, look for a spacer ring that is placed in between the two blocks. I guess there are two possibilties, or the ring in your lens is misplaced or it s missing.



Tomas

[BigMackCam]

Hi, Tomas, and thank you so much for the helpful reply.

OK, I was able to separate the optical and focusing blocks exactly as you describe, by twisting anti-clockwise... no problem at all, just a little gentle effort initially. With the two sections separated, I found the spacer ring - so the good news is that isn't missing.

Re-assembling the two sections, the thread only seems to slot in at one position (although I only tried a few times), so when tightened up it's back in the same place, about 150 degrees around from the top...

[tomasg]

Yes there is only one step on the thread, i think someone must have shimmed down the spacer ring to achieve infinity focus. Not sure about the Jupiter 6 - 2 but my alu version has a M39 mount to which a ring is added to make it a M42. If i am not wrong the Russian M39 mount has a slightly longer flange distance than a true M42, that s the reason why someone would shim down that spacer ring. Good news is you can adjust the focusing part to match the markings on the front. But this means dissasembling the focusing mechanism marking the new position, drilling small holes for the screws in the new position (many of them) and putting back togheter everything. Mind you this means that now the whole lens will be out of allignement on the camera (if i am not wrong), just as the front is now. Another solution is to try to add a shim to the calibration ring, but then you ll probably loose infinity (you can try that by untightening the front, allign it to the back and check for infinity mounted on a camera).

Tomas

[BigMackCam]

My lens is a 1980 M42-mount model - so, as far as I'm aware, there wouldn't have been any need to make adjustments to achieve infinity focus. Maybe the spacer is thicker or thinner than required; perhaps a previous owner needed to modify it to achieve infinity focus on their specific camera (I'm thinking perhaps for Nikon).

I'll have to double check that the lens focuses to infinity on my Pentax and adapted Sony bodies. If it doesn't, that could point to the spacer, I guess. If that's the case, I'll try to figure out a way of shimming it.

Otherwise, if all is working fine as it is, I think I'll just leave it. It's only a cosmetic issue, and really not that important. I don't think it justifies a major re-working, including drilling new holes etc.

Thank you once again for the information - it's very helpful indeed, and much appreciated

[tomasg]

You re welcome!

[tb_a]

[tomasg]

[BigMackCam]

OK - problem solved. I thought I'd explain here in case anyone else runs into the same difficulties.

Checking the lens for infinity focus, it would NOT focus to infinity on my A7II + Fotga M42 adapter, nor on my Pentax K-3 - the latter being something of a "gold reference" for M42 lenses, given that the flange focal distance is exactly the same as for M42 SLR lenses (when a non-flanged adapter is used).

So...

I separated the two blocks of the lens by twisting them apart, as described by Tomas above, and took out the spacer ring. In doing so, I noticed there is quite a big difference between the diameter of the focusing block inner barrel, and the outer diameter of the spacer ring.

Looking more closely at the optical block, I found that there is a very shallow channel (or "groove") that the spacer fits into neatly. By resting the optical section front down on my work-surface, I could seat the spacer accurately in that channel. I then screwed the focusing section back into place... with the result that the markings are now in the correct position, and infinity focus is achieved!

So, it seems that the problem was caused by whoever last serviced the lens screwing it back together without seating the spacer ring in that channel.

Thanks again to Tomas - without your help, I wouldn't have had the confidence to pull the lens apart

[tomasg]

Glad to help, if you read again my first replay the first hypotesis was that it could be missaligned, but not because i am very clever, but because it happened the same to me on one occasion when putting the two parts togheter

Tomas

[BigMackCam]

Thanks, Tomas. I mis-understood your original post; when you said the spacer could be "mis-placed", I thought you meant "lost"... Now I understand