The Kontax focusing

[ruben]

Perhaps the strongest advantage of the Kontax, still beating all, or almost all other manual focusing rangefinders, is in the Zeiss focusing design of these cameras.

No matter how good your lens is, mis focusing will render an unsharp image. If you take most of other fixed lens rangefinders, you can notice that the twist from minimum distance to infinity is about 45 degrees or even less in the case of the compacts.

Against them the twist of the Kontax helical is about 3/4 of a full circumsference, or 270 degrees, six times more than 45 degrees.

This greater rotation enables far greater accuracy when focusing, or if you like it, more field for forgiveness when mis-focusing.

When shooting under good light, the non-Kontax shooter will enjoy from the depht of field of a small aperture, and the shorter travel of his helical. But under poor lighting relative to the Iso film involved, the potatos become hot, due to the very shallow depht of field provided by the widest apertures and the short rotation of the non-kontax helical. Critical focus becomes hard to achieve.

Furthermore, widest aperture plus close distance subject requires a great eye performance from the non-Kontax user.

Here, I believe out of my own, the reason for the small focusing Kontax wheel.
We all know that this small wheel is a kind of fine focusing device. It is worth to notice that if the rotation of the camera helical is about 3/4 of a full circle, the rotation of the small wheel is very close to three full turns.

This means a ratio of 4 to 1. The already great measure of rotating the camera helical can be "increased", or in fact fine-tuned, by four times.

Amazing ! but what do you need it for ? Only today I have got my answer.
If I focus a subject at four or five meters from me, or more, using the helical or the small wheel will make no difference as far as my appreciation of the yellow coincidence.

But if we focus a close subject, let's say at 1,5 meter from us, we will notice a difference. See it by yourself. Focus a close subject with the helical, memorize the image, and then try to "fine-tune" it with the small wheel. You may notice time after time that in such case you can sharpen the coincidence a bit using the small wheel.

When this bit becomes critical ? At close distance and wide apertures.

Now, instead of talking against other cameras, let's take into account some data: For a subject standing at 1,5m using a 50mm lens, at f/1.8, the depth of field is about 9cm.

For the same subject at the same distance and aperture, but using a 40mm lens, the depth of field increases to 15cm, which is not a great gain.

Now think, with which measure of focusing rotation, would you like to face the task.

Cheers,
Ruben

 

[Murray Kelly]

Sorry, Ruben, but I rarely use the little wheel. I find it quicker and more satisfactory to use the left hand to rotate the whole lens barrel. The focus wheel, altho 'more accurate' slows down my shot and I lose a picture if I dwell too long on 'accurate' focusing. I guess, in the long run, I depend on depth of field even wide open. Who knows - maybe I lose a few shots too?

I think one can get too immersed in the accuracy of focus and lose the big picture - get the image and worry about the minutia later.

Murray
Brisbane. Oz

 

[Murray Kelly]

As an addendum - I usually do a close focus then lean back and forth to get the rangefinder better adjusted. I give the little wheel the flick.

Murray

 

[FrankS]

One of the differences between the early 50mm Summicrons (up to the '69 version) is that they had a much longer focusing throw than later lenses. This indeed makes for more accurate focusing, but it is the amount of rotation between infinity and min. focus that determines this, not the little Zeiss focusing wheel.

And Murray is right on about getting the final focus by moving the camera, in close focusing situations.

 

[alecj]

What's this nonsense about Kontax? The word is Contax - look at the camera for gosh sakes. You don't call a Leica a Leika either.

 

[dexdog]

The term "Kontax" is a term of art used by a number of RFF members to refer to the fact that the Kiev is a Contax copy.

I don't concur with the Kontax notion, but nobody is forcing me to use it. A Kiev is no more a Contax than any number of leica copies (Leotax, early Canon, Nicca) are leicas.

 

[wolves3012]

Interesting discussion Ruben. The 270 degree rotation is what allows for fine focussing. The little wheel is quite small, so even though it's on a gearing it's probably no more useful than turning the lens barrel. As personal preference I find the infinity-lock very annoying and I suspect it was only put there to lock the lens when un-mounting or mounting lenses.

As for the accuracy of focussing, this doesn't depend on the RF baselength alone, it also depends on the magnification. If you do the sums you'll find that the Kievs are actually about the same as most of the other FSUs in that regard. Later FEDs (3 - 5) are poorer, the others are pretty much equal.

I'm curently using my 4A and liking it but I'm not thinking it's superior, just different. However, this is most definitely not criticism of your obvious love of Kievs...long may it continue!

 

[ruben]

Hi Folks,
Perhaps I should start writing shorter posts, or find about spirits temperature at RFF before posting the long ones. I find I have been highly misunderstood.

Since I started to fiddle with my Kievs they have aroused my greatest couriosity. Courisousity about why this was designed that way and not otherwise, and specially couriosity about how to take advantage of the many features of this great camera.

One of the devices I always wanted to understand is the function of the small focusing wheel.

The fact that it is a fine tuning focusing aid, is as obvious to the beginner as the fact that focusing with it is highly cumbersome. I don't think there is a single Kontax shooter around the globe that prefers the small wheel over the helical.

But then, why it is there, why it was designed by the Zeiss engineers and later copied by Nikon, Canon and other RF manufacturers ? Was it an excess of perfectionism ? A trick to call marketing attention ? Perhaps Zeiss engineers were silly and never realized it is a cumbersom device ?

It was only after some months of using the Kiev as a street shooter that the mystery revealed to me. The small wheel is no alternative to focusing through the helical rotation of the lens, but an additional highly valuable aid, not found in cheapo RFs.

When it becomes an additional highly valuable aid ?: When focusing to very close subjects using widest aperture. At those situations the accuracy becomes accute.

And how are one supposed to use it ?: You are not intended to start and end focusing with the small wheel, as otherwise the bird will be gone by far. But you can shorten the way at those situations by focusing through the helical and then slightly correcting your focusing with a slight quick and short movement of the small focusing wheel. If Murray, in order to fine-tune his focusing, wants to move his own body forwards and backwards like a praying orthodox Jew - welcome ! but I don't think that in this case it is the small wheel the unpractical.

Of course, there is no point to speak about it, if you never use the widest aperture of your lens, nor other lenses of higher focal length. But it happens that I need this widest aperture a lot, and cannot allow myself misfocusing at close range, the arena I called "the hot potatos" one. Here the depht of field, or the margin of error, is all about only 9 cm, the length of my finger.

Now Murray and Frank, every one is free to use his Kontax as he only wants it. You may have highly good eyes, either by training or by nature, but there is a technical reason and need for which the small wheel was introduced to answer it. You are free to dislike it , but I invite you to try it by the way I pointed here. First focus with the helical, then slightly correct with the small wheel. And, kindly enable me to repeat, this technique is not for every shot, but for widest aperture and close range only. It is not cumbersome at all, and the delay is rather minimal. By the very Contax gripping, your finger is already there. You may not be able to catch mooving subjects, but I doubt that without it you may be able to catch still ones at all at widest aperture and close range.

Let's view it from other angle. I don't own any Kontax. I shoot at shallow light, night light, bus light. I am cornered to use widest aperture. Which camera will answer my needs? Which camera has been designed to equipe me with a special device for accurate focuing at close range ?

Ceirtanly a compact Rf is out of question for its short helical travel. The Lynx 14 is not only too big but no system camera allowing lens exchange. And blah blah blah. But there is one out there: the Kontax. Why the Kontax, because of its broad baselength and its small focusing wheel, designed to answer this problem.

Alec, some hours before starting this thread I had thought about the term Kontax and posted a special thread about it. If you have the kindness and good sense to move your post there, as not to distract attention from the main issues here, I promise to show an equal measure of kindness in explaining why I have coined the term. Furthermore at the corresponding thread I detailed my nonsense to fine grain, so it will be a piece of cake for you.

Dear Dex, by no means the Kiev is a "copy". But you are invited too to discuss it in depth at the Kontax term thread:

http://www.rangefinderforum.com/forums/showthread.php?t=49858

To end this post I call the attention of the Kontax user reader on a method to test weather you need the small wheel at widest aperture, or can do without it.

Pick your Kontax, take a seat, and focus it through the helical to a small object located between 1 and 1,5 meter. Then take your time to memorize the sharpness of this object within the yellow patch. Finally, from this point try to correct the focusing with a slight movement of the small wheel. Do this with different objects. If you find that at each time using the small whell didn't add to the sharpness, then you don't need the small wheel.



Cheers,
Ruben

 

[Spider67]

The term "Kontax" is a term of art used by a number of RFF members to refer to the fact that the Kiev is a Contax copy.

I don't concur with the Kontax notion, but nobody is forcing me to use it. A Kiev is no more a Contax than any number of leica copies (Leotax, early Canon, Nicca) are leicas.

There is a difference between the Kievs and the above mentioned Leica copies as the Kiev has more of a Contax Version than a copy. Manufacturing started with engineers trained by Zeiss employees and some of the parts used in the early production were original Contax parts....So it shouldn't be counted in the same category as the Leica clones. It's a fact that the Soviets liked to copy a lot but later they preferred to take home the factory and the know how....

I think that the Zeiss Engineers had a very stzrange view of the world, when it came to focussing they tried to stand apart from other companies: Look at the Contaflexes up to nr. IV for example: The manual points out that its should be focusssed by using the index fingers of bothz hands

 

[Dogman]

When the light is useful enough to do so, I like to zone focus and let depth of field carry the focus. That way I just use an auxilary finder and I can compose quickly. One thing that I have noticed about the Kievs--they are somewhat optimistic concerning hyperfocal distances. I realize this can be computed based on different sizes of "circles of confusion" or whatever the technical term is, but I find it is usually best to set the focus for hyperfocal distance to an aperture larger than the one I intend to use.