Rangefinder confusions

[Berndt]

Although explained here many times, I still do not completely understand, how those Leica type rangefinders ( Leica, FED2, etc. ) work.

Yesterday, I bought a Jupiter 11 ( 135mm/4 ) at a camera shop and thought, that it should fit at least on one of my four FEDs. I tried the one first, from which I know, that it works precise ... at least with the originally mounted 50 mm Industar lens.

Focussing to infinity, the Jupiter 11 is way out. The optical rangefinder matches where the scale on the lens shows something like 15 meters. But now the interesting thing: Checking the closest distance ( which is 2.5 m on the Jupiter 11 ), both lenses, the original Industar and the Jupiter 11 are showing the same and exact distance on that camera.

Am I going mad ?

[genazzano]

I had a problem with similar camera: The focus was accurate at the closest distance but that fell off as the target moved further out from the camera to infinity. The focus of rangefinders is not optical as it is in SLR's, but rather dependent on the accurate machining of the helicals and a careful calibration of lens elements. In some, often the Russian long lenses, the rate that the helicals move the lens elements from close focus to infinity does not match the change in the real focus of the lens.

I set up my camera on a tripod and added a reliable rangefinder attachment to give accurate distances. I then opened the diaphragm to maximum to minimize the dof at all distances and taped a simple ground glass to the film plane (I actually use a fiber optic faceplate mounted against the film plane which is more accurate than a ground glass plate if such accuracy is needed). I then focused the closest image possible with the lens, in your case 2.5m, marked the real distance given by the accessory RF, and recorded the distance reading that appeared on the lens. I then repeated this using targets at 5 or so different distances from the film plane. This gave me a "real" vs "lens indicated distance". The two numbers ideally should always be the same, but they are often different such as in your case with the Jupiter. You can actually plot the real distance on a X axis, versus the "apparent distance" on the Y axis as indicated on the lens. You can then see graphically how the real vs indicated distances fall off as you approach infinity.

It appears that the Jupiter 11 was set up calibrating the closest distance but the rate of lens movement through out to infinity was not calibrated. On some lenses you can recalibrate the lens so that the closest point can be maintained and the indicated infinity point brought back into agreement with the real distance. However, this is not practical in the Jupiter 11 without dismantling the lens and shimming the right lens group. What I did was more basic and just as accurate in the final analysis: Using a piece of silver mylar tape (used for automobile trimming), I re-labeled the distance scale on the lens so that it agreed with the real distance as measured by the accessory rf.

It really isn't important whether the distance scale on the Russian lens be accurate. It is only important that you know where the real focus is located at 5 or 6 points between close (2.5m) and infinity. In my case, the lens did not focus accurately at infinity but was fairly accurate at all other distances. This is usually not a problem since you need only stop down at long distances to create a dof that brings distant targets sufficiently into focus. It's better to do this than at close distances where the dof is comparatively smaller.

At least 2 of my Russian lenses ended up in the bin due to the poor images as well as inaccurate distance calibration. Also, once you have re-calibrated the lens, the coupled internal rangefinder is no longer useful and an accessory rf is used.

Of course, you can always shoot stopped down to give yourself a good dof and the images may be fine (e.g. f/8- f/11 perhaps).

[Berndt]

That was an interesting read, Genazzano. Thanks a lot !!! I would say then, that the most practically way is to use the lens on the camera, where the inbuilt rangefinder is adjusted best to the real distances and then marking a new scale on the lens. Re-calibrated lens plus accessory RF ... I think, I better use this lens just on a digital camera then. The question is just, how to find out, which camera that would be. It would basically need a perfect adjusted lens for finding that out, right ?

Speaking in mathematical terms, it's an equation with two unknown variables, which can not be solved ... unless we know one of the variables ... or we can define an additional condition, describing the relation between both variables in a different way.

The fascinating thing is, that I do have at least three FED2s, which are perfectly calibrated to their standard lens ( the one, which has been mounted when I got them ). I confirmed that many times by taking pictures with them. BUT ... and that's the interesting thing: IF you would mix the lenses between those three cameras, it wouldn't work. They are obviously only calibrated to the one lens mounted. That actually brings another question up. All those cameras have obviously been refurbished before being sold. A very typical thing and most international sellers from the Ukraine are doing that meanwhile. That's wonderful ... but ... what do those camera engineers actually do for calibrating lens and rangefinder in the way it happens ? What they obviously don't do is, using a standard lens or camera for calibrating the counter part ... otherwise, those calibrations would be the same and lenses could be exchanged. Do you know, what I mean ?

Very difficult to write about that ... getting even more confused ... hahaha ...

[genazzano]

What I did was down and dirty... just to get a good image from a lens that was not standard for a body. In my case, it was a 1938 B&L 75mm telephoto lens for the Argus C2-C3.

If you are inclined then shimming the focusing unit and collimation should be done. Or give it to a repair person who will then likely use a jig that replicates the necessary parameters for the lens and normally end up with the lens that works on any body. Of course you can discard all of this and mount the lens on an SLR and actually see the focused image but it is likely that the lens will not properly focus at infinity with the lens wide open.

Mathematically, you have three parameters, lens position at close distance, at infinity, and the function defined by the helicals which determine the rate of change internally among lens groups with regard to rotation of the helicals. Obviously, the function defined by the gears in the helicals is fixed and cannot be adjusted. Also, the situation is simple if only two lens groups move as you rotate the focusing ring, and unbearably complicated when multiple groups move at different rates such as in zoom lenses that require maintenance of focus throughout the focusing range for all magnifications. I'm too old to do that anymore. I must also warn you that although I designed optical systems, my students were the ones that could actually make them work.

Check the focus of the lens on an SLR throughout the distance range. If the lens remains sharp, then you're fortunate since collimation can be done with shims.

[Stephen]

First I'm not second guessing or correcting the excellent other posts, I worked in camera repair and the answers are not too complex, but do have a few vital points.

There is a basic start point, the mismatches should not occur on a Russian lens with Russian body, or say Leica on a Leica, the problemm of the rate of focus being different only plagues putting one make on another...usually...(there are of course, a few exceptions).

So the Jupiter telephoto should be OK on all Russian FED, and Zorki.

After verifying with a ground glass that the lens in the film plain is truly focusing to infinity, then the original focusing scale engraved on the body of the lens will work 100%(if originally engraved correctly).

This check that true infinity is right on the lens is the first vital point, I cannot stress this enough.


So a body,(any make), that refuses to couple to the scale has a mismatched cam follower on the arm of the internal rangefinder.

The tip of the Russian design is a cam, not a roller like Leica, and can have the tip twisted slightly to adjust it, or the arm bent or adjusted by the screws in the mechanism.

This internal camera adjustment should however be done with great discretion, as if the standard lens works fine, adjusting it to suit the wide angle (or telephoto), will put the rangefinder out for the Standard etc.

In those circumstances each lens must be checked that they focus to infinity, and the standard lens checked, then adjust each lens, which is a complex job on some lenses, not for the faint hearted.

The collar in the back of the lens that acts as the face the rangefinder cam runs on, is on a fine thread which turns in time with the focusing helical, and usually has three set screws that are released, and then the whole collar can be adjusted by trial and error to match the infinity marks to the rangefinder, which remains unadjusted. once infinity is set, the rest follows automatically, but should be cross checked to a target at, say, 10 feet, by use of a ground glass, just to make sure.

The covers most Leica lenses on a Russian, Canon, or Reid or correcting a Russian lens out of adjustment on a Russian or Leica.

So you must have the baseline of trusting at least the standard lens on the body in question, before attempting to match the other lenses to the body.

A very good sound tip is to simply trust the lens makers engraved scales, check infinity is sound, and buy an external rangefinder to find the distances, and transfer the setting to the lens scale,
. This method is easy, you can trust it and it saves all the fuss of adjusting each lens to a body.

It leaves the camera body able to work with it's standard lens, and makes life easy!!..... Also an external long based rangefinder is far more accurate than a built in one, which is why Leica sold so many!!!

Hope this causes no confusion, I was trained on this by the UK's leading Leica Specialist repair person.

Stephen.

[Berndt]

Thanks for all the valuable inputs. First of all, I need to do some checks with ground glass tomorrow. What I can say so far is, that my new lens focusses to infinity in general. I checked that on my digital GH1. It's a good lens, I think, just the DOF is really shallow wide open. I checked that with my GH1. On the closest distance, a movement of a few centimeter back or forward already puts things out of focus. Can a rangefinder be that precise ?




The depth of field depends upon the focal length of the lens and its aperture.

A rangefinder may give you the same image but it has no aperture. It might also not be the same focal length of the lens.
I do not think it can give the same depth of field.

Mickey

[Stephen]

Yes indeed, that is why an external rangefinder is accurate and the setting is transferred. At close distances CM matter for the closest settings. A good rangefinder, external, should have the close settings marked, some don't on cheaper Wata meter types.
Frankly, even the Leica in good adjustment is not wonderful at focusing short telephotos at large apertures, and that is why they spent so much time developing the Visoflex TTL attachments.

The Contax was better, the focus helical was built in the body, and it has a long rangefinder base, as does the Russian Fed 2.

The only Leica type with the full answer was the Periflex, it cannot be out of focus, as it is through the lens focusing, albeit not full frame. The Periflex can also verify the focusing of any Leica lens as to infinity and the scale accuracy, and they backed it up with the accessory focus checker device, a tube that has the Leica thread in one end, and ground glass at the other, built to very high precision, they claimed to .0001 thou or better. Leica made a similar device as well, both are rare items.

They are the basis of testing out any Leica screw lens.

I will get mine out and that a shot of it, it is possible to make one at home, and with care, be as accurate.

Stephen.

[mickeyobe]

Apr 17, 2013 7:39:53 GMT -5 Berndt said:

Thanks for all the valuable inputs. First of all, I need to do some checks with ground glass tomorrow. What I can say so far is, that my new lens focusses to infinity in general. I checked that on my digital GH1. It's a good lens, I think, just the DOF is really shallow wide open. I checked that with my GH1. On the closest distance, a movement of a few centimeter back or forward already puts things out of focus. Can a rangefinder be that precise ?

The depth of field depends upon the focal length of the lens and its aperture.

A rangefinder may give you the same image but it has no aperture. It might also not be the same focal length of the lens.
I do not think it can give the same depth of field.

Mickey

[genazzano]

I always like to see how close I can come before Stephen arrives with the right answers. My compliments on all the help you give.

Ciao! David

[Berndt]

A rangefinder may give you the same image but it has no aperture. It might also not be the same focal length of the lens.
I do not think it can give the same depth of field.

Mmmmh ... a rangefinder has no aperture ? Same focal length ? Same depth of field ? Mickey, what do you mean ? I apologize for my stupidity For me, a rangefinder is a device for measuring a distance/setting the focus or a camera, equipped with such.

I always like to see how close I can come before Stephen arrives with the right answers. My compliments on all the help you give.

Yes !!! Always a lot of new things to learn too. So many words, my dictionary is giving me just nonsense or unsatisfying results. But google is a blessing nowadays. I often provides an understandable image of a specific word, where an ordinary dictionary fails.

[Stephen]

Leica Focus Checker.







Shots above of the Periflex, (Leica) focus checker, a tube with a ground glass set 28.8mm from the flange, so that any screw lens can be fitted and checked. Corfield also added a blue frame, and removable collar to allow it to be used in a macro set-up, substituting for the camera during set-up. The ground glass is examined with a Lupe lens or magnifiying glass.

A home made one could be made from a M4/3 cheap Leica adaptor for the screw end, a suitable plastic or metal tube glued on, and the other end adjusted to be 28.8 from the screw flange, and then a ground glass epoxied on ground face inwards. The glass could be an old UV filter, ground with fine car valve grinding paste on one side. It might be better to then refit the old filter ring to protect the glass edge.
The 28.8mm must be checked with a depth gauge, a vernier caliper, or micrometer, as accurately as practical.

If the front screw part is a Micro M4/3 adaptor type, then the Leica screwed part is held in by tiny set screws around the edge, and very fine adjustment could be done with very thin paper to shim it, under the screwed part, and then re-do up the set screws.
Thin cigarette papers are one thousandth of an inch thick approx.

Stephen.

[Berndt]

Stephen, why don't you live in my neighborhood ? Then I could rent such valuable tool for an afternoon. I actually wanted to do the ground glass tests today, but trying the fourth and last of my FEDs, there was hope. My new Jupiter seems to match the rangefinder of this camera perfectly at infinity and also on closer distances ( just by guess ). So I decided to put a film in and try it the simple way by taking pictures. The film is not full yet ... but I have a small hope, that this lens might work on this camera just like that. If not, I might need to start from scratch and read all these posts from the beginning ... hahaha ... wish me luck

[retina]

I've got a similar device, also M39, not a nicely made, but does the job, except this one has a distance of 44mm from screen to lens mounting flange, so I'm assuming it is for a Braun Paxette.





Regards, Chris

[Stephen]

Being Paxette flange distance, it may have been a Braun factory made item, or made by a specialist maker for the Camera repair trade.
M42 Pentax screw fit focus testers turn up occasionally, Leica made them for M39 thread, as did Corfield Perflex, and Zeiss. Most lens makers made them for testing lenses in the factories.
Ken Corfield made a short extension ring for the Periflex checker, for M42, and a version with Exakta bayonet, which are exceedingly rare. Ken Corfield was the official Ihagee Exakta importer to the UK, as well as making the Periflex cameras.

Stephen.

[Berndt]

BTW Stephen, you mentioned an M4/3 Leica adapter above. Is there actually any reason, why I shouldn't simply use my M4/3 camera for testing the lens then ? I would assume, that people, who made this adapter, manufactured it as a pretty precise instrument ( why else would I have needed to pay 50 bucks for a simple metal ring then ? ) and also the focussing on a digital camera ( I use an "old" Lumix GH1 ) is pretty precise, especially if using the inbuilt digital enlarger. So I would assume, that both, camera and adapter are manufactured at a much higher industrial standard than I could ever do, by making my own home built tester ... or am I wrong in this ?