View Full Version : Question About the Kiev Helical Lens Mount
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
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
06-07-2007, 05:12
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
06-07-2007, 05:14
just noticed this thing publishes our ages. scary......
........... 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
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
06-07-2007, 05:50
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.
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
06-07-2007, 07:52
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.
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 ?
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.
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
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
06-07-2007, 11:45
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 : ) =
Many thanks Rick for your time and persistance !
Cheers,
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
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
06-07-2007, 17:25
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.
: ) =
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.
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
rick oleson
06-08-2007, 04:13
I can only speak for myself, but I never, ever even look at the engravings on a lens barrel. Let's assume for the moment that they are perfect, so you decide to adjust your lens for perfect accuracy at the convenient distance of 1 meter.
1 meter from where? The front of the lens? The film plane? Could be either one, or something else, it was a decision made by an engineer who is now long dead and we can't ask him. The classic practice was to measure from the film plane, but how are you going to line your measuring tape up with that? And how accurately can you measure with a tape? If you're off by an inch at 1 meter you will be off at every distance.
Now, let's consider infinity. If you can establish a correct infinite target, you don't care where it's measured from - infinity is always the same. Your focusing travel stops there, so you don't need a number on the lens to tell you where it is.
Now, again, let's consider how you take pictures with the Kiev: Do you carry a tape measure with you, anchor one end at your camera position, walk to your subject and read the distance, and then set that distance on the engraved scale on the lens barrel? No. You stand where you are, turn the lens mount until the 2 images in the rangefinder coincide, and then take the picture. So, what difference does it make to your pictures whether the engravings indicate the actual distance to the subject? The thing that establishes your focus is the rangefinder, so what is important is that the rangefinder and the lens agree.
I have no doubt that the engraved markings on a Kiev, a Contax or any other camera are accurate. But it would make no difference at all to you if they were not even there, because you don't use them. The camera needs to be adjusted the factors that actually control your picture, rather than the ones that you never actually use in practice.
The only cameras in which the engraved markings are important in use are those which do not have rangefinders. In these, you generally guess the distance and set the distance on the lens to suit your guess. In this, it is easy to see that the larger potential source of error is your guess, not the accuracy of the markings. In the case of a scale focusing camera as well as an SLR or a rangefinder, I always adjust both the lens and the viewfinder at infinity. If it was made well (or even competently), the engravings will then be correct automatically.
There ARE in fact two instances of the highest importance in which we disregard what the range finder may indicate and use instead our distance scale.
One, is when we are calibrating the range finder itself. The Contax and Kiev provide us the means to calibrate both the infinite AND the shortest distance. If the infinity is Ok at our viewfinder, but the shortest distance is not, then all what is in the middle will be wrong too.
I insist about it, because there are many things that with the pass of time made our Contaxes and Kievs "outdated". We don't have there AE for instance.
But what we already do have there, I want to use it to the best, to exploit it at the fullest.
The other very current use of the distance scale, instead of the range finder, is when we are using the common technique of depth of field. Then when we happen to make a pic of a close subjec - better our distance scale will be telling us the truth. More over if we are using the DOF technique with the standard lens.
The TRUTH for us is absolutely shown at our negatives, which are the practical side of the whole thing. This means that for us, ANY lens set by the distance scale to 1meter MUST give us critical focus in our negative, OR FILM PLANE. Otherwise we should check what is wrong. I remind I am speaking about Kiev and Contax only.
Finally there are other instances, more rare but still necessary, in which we will not rely on the range finder, but solely on our distance scale: when we check our gear, i,e, the helical mount shimming and our lenses.
If the shimming of our helical is wrong, then the infinity will be wrong, as well as whatever the distance scale and our range finder will show. The range finder prism coincidence depends upon the right helical shimming in order "to tell the truth", it is not independent. With wrong shiming we still can obtain range finder coincidence at the infinity, but it will be wrong too.
As for the lenses, it happens that the most severe test we can do for knowing what we have, is to test test them wide open at the shortest possible distance, let's say 1 meter. Let's suppose we have several standard lenses for our Kievs or Contaxes and want to know which one is best. We will put our camera on a tripod with a subject at 1 meter and our lenses at widest aperture. Will we then use the range finder coincidence or the distance scale ?
If our range finder has been accurately calibrated, and our helical mount too, we will have our range finder happily agreeing with the distance scale. But from practice we know that our eyes tend to byass our identification of rangefinder coincidence, so using the distance scale will be more practical.
The distance scale of our Kievs and Contaxes, on an accurate shimmed helical mount is the original. The range finder the xerox copy. The latter should match the former, must match it, since as Rick correctly and symphateticaly says, we are not walking around with a measuring tape.
But for CLA, when we must split hairs, we should have things re-built around the original, not the copy. All what I have asked, wrote, and thought in this thread, has been in view of the comming CLA to be exposed at the "Kiev Project".
Cheers,
Ruben.
PS
Regarding the Kiev Survial Site, it has been my first technical introduction to the Kievs. I owe everything to Russ. I have praised the KSS since its appearance, so many times up to the point that if I do it once more I am afraid a gang of RFF members will specially come home to beat me.
If my memory doesn't fault me Russ shows there a kind of digital caliper for measuring the distance from the helical mount to film plane, plus some exchange he had about it with Henry Scherer.
rick oleson
06-08-2007, 15:19
Hi Ruben:
If I thought that the engraved scale was a better guide than the rangefinder I would have saved quite a few dollars in camera bodies over the years. The shimming is tested with a groundglass in the film plane, and the rangefinder matched to that, both at infinity and at closer distances. If the lens agrees with its engraving but not with the rangefinder in any of these cases you will not get a well focused picture. When using the engraved scale for DOF bracketing, it does not matter if the scale is actually correct: you focus on the far and near points using the rangefinder and then set the lens midway between the 2 positions, and stop it down far enough that the bracket covers that difference. If the indicated distance is 8 feet but the actual distance is 9, the engraving was wrong but the picture still is right because you were careful in your CLA to match the rangefinder to the focal plane. I don't know for sure that I have ever used the distance markings for actually determining the focus point on a camera that had a proper working rangefinder... maybe once or twice, but I can't think why it would have been.
I think between this and my previous posts and the website links, I've laid out pretty much everything I can think of to say on the subject.....
take care : ) =
Hi Ruben:
............I think between this and my previous posts and the website links, I've laid out pretty much everything I can think of to say on the subject.....
take care : ) =
Hi Rick,
Excuss me for having "milked" you to the last drop, but only upon your last post I realize what do you actually do, and it is a new approach for me.
If I understand you correctly you set your range finder both for infinity and for shortest distance using a ground glass. This is somewhat new for me, as what I did till now is to fit the range finder coincidence to the helical distance markings and afterwards check both extremes with the ground glass. An slr screen in fact.
Well, your approach goes very much along my axioma that the truth is in the negative.
New grounds for me to think about, I am happy.
Cheers,
Ruben
rick oleson
06-08-2007, 16:08
Yes, that's correct: rangefinder must match groundglass, engravings do not matter, regardless of the distance involved.
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