Question About the Kiev Helical Lens Mount

[rick oleson]

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.

 

[ruben]

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]

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 : ) =

 

[ruben]

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]

Yes, that's correct: rangefinder must match groundglass, engravings do not matter, regardless of the distance involved.