Question About the Kiev Helical Lens Mount

[ruben]

Hi,
I have found diverging opinions about dismounting the internal cylinder of the Helical Lens Mount. One favours it on behalf of good cleaning, the other dis-recommend it on behalf of the hardness in threading it back accurately.

I happen to favour by now the dismounting, on the basis that the little protrusion stopping the internal cylinder at infinity, takes care of telling us our re-mounting has been accurate.
But I would like to hear other opinions about my theory.

Thanks,
Ruben

 

[varjag]

The problem with remounting is not getting the helical together, but coupling it in same position to rangefinder gearing. You miss one tooth, and your infinity is off. This is well described at Russ' site.

It is still a good idea to give helical a clean and relube though, if one's serious about CLA.

 

[rick oleson]

I don't recall any particular difficulty in getting it back right, since it's only a single helical - the ones that are tough are the double helicals in some of the non-rotating lenses, and the worst of all are the LTM teles with their RF coupling cams - getting the lens and cam all back in right is a real chore.

🙂=

 

[rick oleson]

just noticed this thing publishes our ages. scary......

 

[ruben]

........... You miss one tooth, and your infinity is off. This is well described at Russ' site.
...............................

Hi Eugene,
My question is in other words: Provided the infinity lock closes or stops the internal cylinder while the distance scale is showing dead on infinity - will this be the sign I have not missed a single tooth ?

Cheers,
Ruben

 

[40oz]

just noticed this thing publishes our ages. scary......

you can hide it under Edit profile in your user CP.

I'm not sure why one's age is important data.

 

[rick oleson]

The gearing is between the lens mount and the rangefinder prism: if your rangefinder is correct at infinity when your mount is at infinity, then you're good.

 

[ruben]

Yes Rick, but the whole thing we are talking about is wether the infinity shown at the distance scale after re-mounting the cylinder is indeed infinity. From here onwards we can proceed to adjust the rangefinder coincidence accordingly.

Cheers,
Ruben

 

[TVphotog]

I usually make a mark on the brass gear just to the left of the lens mount. If the mark is in the right spot when I rethread the mount then I am good. If not then I take it out and try again. On the 2A that I removed the mount from I found that someone else had done the same thing, but not gotten the mount back in right. It took a couple of days, but I believe that I have it fixed. I have to get a piece of glass and check the focus at the film plane. At least the rangefinder coincides with the distance scale now. Before it was way, way off. Gonna try and check it this weekend. My final thought is that like any other operation involving these cameras, as long as you are careful and double check you work, it should not present a problem.

 

[ruben]

Ok, I will put the question in another way.

When we thread the internal cylinder into the camera mount, the fixed part, we are rotating it. As we rotate it, it goes inwards. The question is wether the thread is built in such a way that we can rotate an extra full turn inwards (too much) and the infinity lock will not notice us, engaging as usual.

Or in the other way, wether we can rotate a full turn less than the necessary and the infinity lock will still engage as if nothing had happened.

Hence my question: is the infinity lock good enough designed to mark us the accurate infinity when we are threading back the internal cylinder ?

Cheers,
Ruben

ps
The infinity locking function is composed by two parts. One is the loose arm whose extreme we find behind the small wheel, and the other is the thin hole, which is fixed within the non rotating part of the focusing mount. Is this thin hole thin enough to not allow any error when re-threading the cylinder ?

 

[varjag]

Yes Ruben, if I understand what you're saying correctly, the infinity lock is good enough for that.

Also, the helical is two solid parts, one with index mark and one with distance scale. There's only one way the the two can align.

 

[ruben]

Thank you Eugene,

The source of my question is that when you unthread the cylinder for cleaning, in fact there is very difficult if not impossible to follow the exact point when the cylinder separates from his housing. And as dificcult to thread back from the exact point you wish.

Cheers,
Ruben

 

[ruben]

The problem with remounting is not getting the helical together, but coupling it in same position to rangefinder gearing. You miss one tooth, and your infinity is off. This is well described at Russ' site.

It is still a good idea to give helical a clean and relube though, if one's serious about CLA.

Hi Eugene,

Russ has refered me back to this posting of you, and perhaps I have not propperly understood it, or not propperly explained myself.

If I understand you about the abovequoted sentence, you are talking about a situation in which our rangefinding is well aligned and we want to dismount the whole helical lens mount for cleaning. Then obviously, " You miss one tooth, and your infinity is off".


But what I was refering to is the other situation, in which we have not aligned our rangefinding yet, and we are first cleaning and remounting the helical mount.
Then my preocupation, which now I see I didn't mention, was about the rotating cylinder vis a vis the film plane. It is in this context that I am asking if the thin hole receiving the infinity lock arm, can be used to comfirm our rotating cylinder went back into place.

Could you re-comfirm or deny ?

Excuss me if I am abusing of your time, and thanks beforehand,
Ruben

 

[rick oleson]

Ok, I will put the question in another way.

When we thread the internal cylinder into the camera mount, the fixed part, we are rotating it. As we rotate it, it goes inwards. The question is wether the thread is built in such a way that we can rotate an extra full turn inwards (too much) and the infinity lock will not notice us, engaging as usual.

Or in the other way, wether we can rotate a full turn less than the necessary and the infinity lock will still engage as if nothing had happened.

Hence my question: is the infinity lock good enough designed to mark us the accurate infinity when we are threading back the internal cylinder ?

Cheers,
Ruben

ps
The infinity locking function is composed by two parts. One is the loose arm whose extreme we find behind the small wheel, and the other is the thin hole, which is fixed within the non rotating part of the focusing mount. Is this thin hole thin enough to not allow any error when re-threading the cylinder ?

Sorry, Ruben, I wasn't clear:

You don't have to worry about the helical itself, if it locks in at infinity it's correct. This is only a single helical, for it to come around to the infinity mark at any "wrong" position it will be so far off fore/aft that it will look obviously wrong. There are multiple starts on the helical, but if you get in on the wrong start it will be very obvious when you get it in to the infinity point. The only thing you have to use particular care with is the gear connecting the helical to the RF prism... and even that is not so difficult.

rick : ) =

 

[ruben]

Many thanks Rick for your time and persistance !

Cheers,
Ruben

 

[ruben]

I am very curious. Why do you align the rangefinding first and re-mount the helical afterwards ?

Perhaps my logics are too formal, but my understanding says that the rangefinding alignment should mimick the "real thing", which is the movement of the lens, via the helical, forwards and backwards to film plane, as if the range finding was just an aid for not using the distance scale, and not the opposite.

So I am truly curious, about the why of your proceeding. Would you like to elaborate ?

Cheers,
Ruben

 

[varjag]

Ruben, I *think* (can't remember 100%) that the helical has more than one entry. But it shouldn't be possible for the helical to screw down to correct interlock at infinity if the entry was wrong. At least I honestly can't ever remember such a problem with my limited experience.

Now I see Rick and f2eyelevel posts seem to refer to the same thing. I can only confirm that 🙂

So in short, if your helical when screwed down shows infinity, and you mounted the helical asembly with original shims (given that they were correct in first place), you should have correct film-to-flange distance.

As for RF adjustment, making helical align with cogwheel properly at infinity *is* the adjustment. Pre-war Contax type rangefinder, given correct assembly, does not require another adjustment points: that's a virtue of very robust and straightforward coupling to lens movement via the helical, combined with use of single monolithic prism. Once it's on spot, it is rather hard to knock out (lots of firsthand experience here).

There are other possibilites of aligning the RF, mainly involving adjustment of the wedge lens, but it doesn't feel like they were designed in.

Hope it helps!

 

[rick oleson]

Cool video!

Adjusting the rangefinder and the lens/lens mount are two separate considerations. Of course the lens wants to be correct at infinity when it is at that mark, but when you actually use the camera it is the rangefinder that you are focusing by, not the engraved scale - so having the rangefinder match the lens is more important than having it match the engravings.

The approach that I take is to get the lens correct at infinity, and to get the rangefinder correct at infinity. Usually if it hasn't been tampered with, the camera's mechanism will then take care of the other distances, but there are adjustments in some that can throw them off if disturbed, so you should also check a close distance to verify that it is also correct at that end. In doing this, though, you do NOT measure the distance and compare it to the engraved number on the lens mount.... you put a groundglass in the film plane and check focus to make sure it's at the same point as indicated by the rangefinder. Again, it is the lens image and the rangefinder that must agree, the engravings are just a general guide.

I have methods for determining the correct infinity positions for both the lens and the rangefinder without having to go outiside and look at the moon or a distant lamp post: I have found that I am often doing this task with the camera half-disassembled, and taking it outside in the dark is a good way to lose pieces forever. Rather than try to explain how I do this, I will just invite you to look at http://rick_oleson.tripod.com/index-123.html where I have been able to include drawings to help show what I'm doing.

: ) =

 

[Wayno]

I usually make a mark on the brass gear just to the left of the lens mount. If the mark is in the right spot when I rethread the mount then I am good.

That's what I remember doing - got it from Russ' site no doubt.

As Rick says, if the image at the film plane and the rangefinder match at infinity then all is usually good. The distance engravings are just a rough guide.

 

[ruben]

Hi Rick and Each of the nice folks around having taken place at this thread, and those still to come.

Rick, with you last post here, we directly arrive to the question of questions, the song of songs, the mother of all battles about Contaxes and Kievs: what is our starting point for starting measuring the best possible -accuracy of our Contaxes and Kievs ?

We stand before our newly arrived Kiev or Contax.
-The helical shims may have been changed by the past user of the camera.

-The lens comming with the camera may have not the best internal shimming as well, and mislead us for when using other lenses.

-The rangefinder arrangement may be accordingly misleading, or outrageously misleading.

So what is our starting point to look for when organizing this sub-mini caos ?

My theory, based only on my nose, and extremely limited experience, is that talking all the abovementioned into account, the starting point should be our reliance on the distance ring markings, which have been designed for extreme accuracy.

It seems to me that in contrast to, let say, a Canonet, or a GSN, or another of the like, with Kievs and Contaxes the distance markings must be absolutely accurate, this being part and parcel of the strongest side of this brand of cameras.

The distance markings, after adjusted to fit film plane, should be today the basis of the whole building. Another advantage of this approach is that the Contax distance markings have not changed with time, nor degraded in Kiev, or changed by past users.

Now, as I said, I base this theory only on my nose deduction, and will be very glad for the contribution of any other member, on this highly important issue, Rick included of course. With the explanations of every one we are going to gain a lot, I am sure.

Cheers,
Ruben