M8 rangefinder DIY and other myths?

[dante]

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Is rangefinder self-calibration via the infinity adjustment really a workable solution?

 

No!

 

I see a lot of talk here about how it is "easy" to use a 2mm hex key to adjust the infinity setting, but that is a hell of a lot harder to do correctly than anyone lets on. You can make things vastly better with one lens at a time, but operationally, there are a few difficulties with multiple lenses - as I learned when I had to make an emergency field adjustment (to get a 90 Summicron to work). The point of this discussion is that it might take a few minutes to adjust your camera for a single lens but that you are unlikely to succeed at achieving perfect focus across multiple lenses. In other words, throwing a hex key in the bottom of your bag is not going to lead to any kind of meaningful field fix.

 

Theory

 

Start from the proposition that all Leica-mount lenses have a tolerance in the brass ring (cam) that contacts the RF roller in the body. Continue along with the assumption that all Leica lenses have the RF cam timed to simulate a nominal 50mm lens (it’s actually a little longer than that, but that’s a different discussion). Next consider that Leica makes a finite number of focusing mounts for each type lens (which to some degree cancels out the fact that there is a tolerance in focal length between optical units). In a completely unforgiving environment like 18x27mm digital, you are going to be lucky to have the focus perfect with one lens, much less a collection of three or more lenses.

 

Praxis

 

With this in the background, a lot of people will “tweak” their M8 body to work "perfectly" with their favorite lens. Whatever the surface appeal of this, the calibration process is both miserable and deleterious to the focus of other lenses.

 

First, the 2mm hex nut has a ton of inertia in it - enough to cause a 50mm long steel hex key to flex before the nut actually moves. This causes the nut to "snap" from one position to the next and by the time you can feel the hex nut move, it has already moved too far. By the way, the proper adjustment is often much, much less than the "2-3 degrees" I see recited here. The ideal way to adjust the nut is to tap on the hex key, but this threatens to pop the key out of the socket and damage the socket. It is also exceedingly dificult to do when you are trying to keep the arm immobile (see below).

 

Footnote: you need a very, very good hex key with a short arm that is perfectly hexagonal. Cheap hex keys often have damaged short ends as a result of how they are manufactured.

Second, it is hard to adequately immobilize the RF lever arm when making adjustments that induce nearer focus (i.e. moving the hex key toward the RF window to make the camera focus "nearer"). It's a tough mechanism, but even as someone who works on Compur shutters occasionally, it makes me nervous.

 

Third, you have to check every distance with every lens (and multiple apertures) every time you turn that hex nut. What makes your Summilux 75mm work unbelievably well can do incredible violence to the near-focusing accuracy of your other lenses - like a 35mm Summilux ASPH. The problem is that with Leica's acceptable tolerances in RF cam position, fast lenses will actually be all over the place. Then you have to account for focus shifts in lenses. Not fun.

 

Fourth, you will see variations in how your lenses line up at infinity. This is due to variations (within tolerance) in RF cam position. Most of the time this is not a problem. But be aware that RF errors work a much more severe effect as the distances from the camera increase. The idea is to keep RF error low enough that it is caught up in the depth of field of the lens as the distance increases.

 

Fifth, "balancing" your lenses will result in the DOF being strange with some. In the normal case, DOF is 1/3 in front and 2/3 in back of the focused point. When you attempt to reconcile various lenses, you will end up that some are 2/3 in front of the focus point and others 1/2 in front. The more of your DOF is in front of the subject, the less DOF increase you will get from stopping down.

 

At the end of the day, if you have a lot of lenses, you are really going to have a headache. This is not a process that takes a couple of minutes - settle in for several hours if you want to do it right. I ended up being forced to do it in the field - which beats 5 weeks at Leica - but it was unpleasant.

 

Tips

 

If you have to undertake this project (I only did by being forced to), I would recommend the following NOTE: We are all adults. I am not responsible for any negative results you get from applying these tips.:

 

1. Understand your sharpness “goal.” What is the minimum level of sharpness you are willing to accept from each of your lenses on a flat subject at minimum aperture? One measure might be picking up the grain on a piece of satin aluminum at 1m. Or picking up the thread pattern in a dress shirt at 2.5m. Or the aggregate in cement at 5m.

 

2. Understand your DOF goals. What is your most important lens? How do you want it to behave?

 

3. Buy good tools. A good 2mm hex wrench costs a few dollars and is much less likely to damage your camera than one from the dollar (EURO) store.

 

4. Do your verification with a magnifier AND without one. Sometimes the magnifier impacts results. Likewise, if you use contacts and glasses, try your final adjustment with both.

 

5. Use a variety of subjects. You don’t always shoot flat objects; don’t test on flat objects. You are part of the system. How you focus will always influence the results.

 

6. Use flash. It might not be the best light outside when you try to fix your RF. Don’t kid yourself that a tripod is very useful for checking the RF. You will hand hold the camera in real life, and you need to check the camera against numerous real-world objects to make sure it works. Flash helps you move around – and because it creates a high effective shutter speed, it eliminates motion blur. I used a Nikon SB-20 with gaffer tape over ¾ of the head, in manual-power mode, with the head set to bounce off the ceiling. At 1m with a 75mm Summilux at f/1.4 and ISO 160, the power factor is 1/16.

 

7. Bracket focus. This will help you determine what is going on with flat subjects. Initially focus the subject. Move the focus a little bit nearer. Shoot. Put the RF spot on. Shoot. Nudge focus farther away. Shoot. Then check all three at the focus spot at 1:1 by holding down play as you press the arrow buttons to switch shots.

 

8. Do not depend on the viewscreen. The LCD can help you understand whether something is more in focus than something else, but the quick-and-dirty demosaic-ing algorithm in the camera can get screwed up by certain object textures. Double-check on your computer. In general, you are getting close to perfect when the camera screen at 1:1 produces a moire on something like a finely-textured fabric.

 

9. Watch the eyestrain. It may take several hundred shots to align a rangefinder – so give your eyes time to rest now and then.

 

10. Understand that ultimately, you may need to use a special technique with one or more lenses. For example, with a fast telephoto, plan to focus at the nearest distance where the RF looks like it lines up. Or you might want to do your precision focusing from far to near (or vice versa).

 

Prospects for coupled RF

The thing I see from this is that the mechanical rangefinder is a dead-end technology with fast lenses, particularly if sensor resolution goes up. With digital, the tolerance for error is almost less than the practical unit of rangefinder adjustment - and acceptable manufacturing tolerances in the population of manufactured Leica lenses (even in the last 20 years) lead to inconsistent results on sensor. This helps explain why Leica is bringing out slower Summarit lenses.

 

Leica USA seems to be resistant to adjusting the cams on lenses that are “within spec,” meaning that you will always have one or two “special” lenses that require a special technique. I can see their point. Some error has to be tolerated; otherwise, the company could be sucking up warranty costs related to 30 to 50 year-old lenses rather than the M8 itself.

 

The solution to all of this is probably to replace the expensive RF system with some kind of passive focusing indicator/confirmation similar to that in a DSLR. This would have three principal advantages. First, it would allow the elimination of the mechanical RF coupling and thus eliminate a tolerance that could cause errors. Second, it would remove play in the RF system’s mechanical components. Finally, it would eliminate vagaries of human eyesight and eye position as sources of focusing error. Where you would detect the image is the hard part; maybe off a mirror on the front shutter curtain, with the system calibrated to assume an image plane sightly behind that.

 

Alternatively, Leica could offer a remanufacturing service whereby it would profile the lens cams by focusing them at multiple points and then computing the correct offsets along a curve - like a modernized version of Linhof RF cams for specific examples of lenses.

 

Or Leica could sell M8s with "best match" sets of 3 lenses. Or adjust your M8 to be a best match to 3 of your existing lenses.

 

Now where is that aspirin?

[blakley]

Exceptionally useful & sensible post, as usual Dante. Thanks. My temptation has been to send the whole kit for calibration at some point & put up with the delay and expense, and you've certainly reinforced that notion. I love the tags you've added to your post, by the way!

[Kent10D]

Sounds like you had a bad experience.

 

Perhaps one reason for the difficulty is that you tried to make a fairly critical adjustment in the field. I don't think anyone here would actually recommend doing it that way (although I'm sure some have). If you're critical about the results it will requires a bit of concentration, solid support, appropriate tools, an easy-to-focus target, a clean environment, and a means to accurately check the results, as you mention. There will always be some lens-to-lens compromise, that's just the nature of the beast, and only you can decide how that compromise should be made for your specific needs, which I guess is why a lot of people prefer to make the adjustment themselves (in addition to avoiding down time). And, yes, if you have a number of lenses it can take a fair amount of time to reach a happy compromise for them all. I certainly wouldn't call it "simple."

 

You might need to set aside a half a day or so to carefully set that one simple parameter for, say, 5 or 6 lenses. I found the results to be well worth it.

 

But of course, as they say (and I only learned this acronym recently): YMMV!

 

Sorry to hear about your travail, hope you sort it out.

 

Cheers,

[dante]

Kent - the basic field adjustment was simple. That was getting a 75 Summilux to work adequately for a few hours. It was the "getting things really right" later that took the work described in that post. That, of course, was done under controlled conditions and it took, as you described, almost an entire day. Not fun.

[Kent10D]

Kent - the basic field adjustment was simple. That was getting a 75 Summilux to work adequately for a few hours. It was the "getting things really right" later that took the work described in that post. That, of course, was done under controlled conditions and it took, as you described, almost an entire day. Not fun.

 

Ah ... the 75 'lux.

Coincidentally that's the very lens that precipitated my day (or two) of adjustment too. Quite a little troublemaker that 'lux. But when it's done properly it's nice, isn't it? My only concern now is how much of a knock, or whatever, does it take to throw the whole mess out of whack again? Not that I plan on subjecting my M8 to any serious knocks, but these things happen.

[Tony C.]

Dante,

 

You have delved much more deeply into this issue than most, and I don't dispute many of your points. However, I must say that when I calibrated my M8 to infinity, it did, in fact, seem to work well for all of my lenses (Noctilux, 28mm 'cron, 35mm 'lux, and 75mm 'cron).

 

Now it is true that I have not done any serious testing to confirm my claim, but from a practical standpoint, none of the images produced by my lenses have shown signs of any focussing issues.

 

Finally, I believe that you have failed to mention a crucial variable in the adjustment process: the importance of using a truly distant point to focus on–preferably a celestial body. I did notice a significant difference in the results achieved between my initial adjustment (using a point 100-300 yards away), and using a star the second time around. The accuracy improved greatly after I used the latter approach.

 

Regards,

 

Tony C.

[jaapv]

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I think there may be a misunderstanding about this adjustment. That goes for the M8 and any M camera from the M3 onward. It is not meant to adjust the whole rangefinder system. The lens-camera interface, i.e. the helicoid-roller connection it the most prone to wear, slightly bent (!! ) arm etc. To compensate for these problems in the field and to bring the basic geometry into tolerance this quick-and-dirty system was incorporated. To advocate it as a cure-all for focussing problems or as a final exact tweak for critical lenses, well, Dante is 100% right. It was never intended that way.

[Kent10D]

I think there may be a misunderstanding about this adjustment. That goes for the M8 and any M camera from the M3 onward. It is not meant to adjust the whole rangefinder system. The lens-camera interface, i.e. the helicoid-roller connection it the most prone to wear, slightly bent (!! ) arm etc. To compensate for these problems in the field and to bring the basic geometry into tolerance this quick-and-dirty system was incorporated. To advocate it as a cure-all for focussing problems or as a final exact tweak for critical lenses, well, Dante is 100% right. It was never intended that way.

 

Hi Jaap,

 

You're probably right, but with a little care it does the trick in many cases, and being that it's the only easily-accessible parameter, people are going to use it that way for sure. If it was a simple matter of taking the camera down to the local Leica outlet, if such a facility existed, and waiting half an hour for the job to be done, that would be wonderful! But with multi-week turnarounds I can undertand why people take the risk. And to be sure, it is a "proceed at your own risk" type of thing. So I certainly wouldn't "recommend" it to anybody, but it worked for me.

 

Of course it would be much nicer if it wasn't necessary ...

 

Cheers,

[marknorton]

I agree that the mechanical rangefinder technology is creaking with the dual demands of digital and longer and faster lenses.

 

The only way to ensure lens interchangeability is to calibrate cameras and lenses against independent standards, not against each other. Adjusting the camera to work with one particular lens runs the risk of problems with others.

 

For the camera, using the lens flange as a reference point, there's a defined relationship between the position of the roller and the distance at which the rangefinder image is then coincident. It would be very interesting to measure this over a number of cameras to see what sort of spread there is across unadjusted cameras.

[jaapv]

The main indication to use this adjustment is when all or most lenses show a non-coincident rangefinder patch at real infinity. The adjustment is easily done in that case. Everything else, especially trying to adjust near focus this way is a lottery. Dante explains that at length in the OP, and he is right.

I wonder about the round-trip to Solms though. There is nothing different between the M8 and other M cameras mechanically. A good Leica technician and an optical bench can do these adjustments, including shimming any lenses if needed. The only difference is he would not use a matte glass in the film guide, but a tethered laptop.

[stunsworth]

There is nothing different between the M8 and other M cameras mechanically

 

Are you sure about that? Leica UK no longer adjust rangefinders. When I was there last I was told that there were 6 adjustments made when calibrating a rangefinder - which I took to mean it was adjusted at 6 different distances.

[erl]

There is nothing different between the M8 and other M cameras mechanically. A good Leica technician and an optical bench can do these adjustments, including shimming any lenses if needed.

 

Jaap, last week the local importer for Leica examined my M8 + Noct. for backfocus problems. He stated that he could not measure or make corrections because the jig(s) he had were of a different thickness to the M8 body so he could not fit my M8 into his (analoge M) equipment. My M8 + Noct is all now on its way to Solms.

 

I have no way of verifying his statement, but that is what he said, unfortunately.

[jaapv]

Hmm. it is possible that jigs etc. don't fit. I meant, however, external repair services, not the official Leica channels. Strictly speaking that is one step up from DIY Leica has a policy of doing all work on the M8 in Solms. That is probably justified, given the complexity of the camera and their reputation riding on it.

[Shootist]

Are you sure about that? Leica UK no longer adjust rangefinders. When I was there last I was told that there were 6 adjustments made when calibrating a rangefinder - which I took to mean it was adjusted at 6 different distances.

Not sure it is adjusted AT (@) six different distances. When they state there are 6 adjustments made that can mean that there are 6 adjustment points. I can think of 4 and see 3 inside the lens mount. Verticle alignment (Behind the red dot), Near focus point, Infinity focus point and the close focus stop. The last 3 are what can be seen inside the mount.

There may be 2 internal adjustments under the top cover and they could be the frameline indicators and how they line up for each individual lens focal lenght.

 

Other then those 3 focusing adjustments, near/infinty and close focus stop there isn't any others that I can think of.

If the camera is properly adjusted for infinity and near and the stop is set right then everything else is done on the cam of the lens. There is rally only TWO focus adjustment. The roller the lens cam hits and the arm mounting point. The only way there could be a third adustment is IF the shaft that rotates when the roller and arm move is connected to another concentric cam.

[dante]

In the days where a 50/2 lens was the standard, Leitz invented a "standard lens" against which the RF was adjusted at infinity. The "standard lens," as DAG informs me, is an all-metal affair. I don't recall offhand, but I recall being told by someone that the eyepiece is viewed under very high magnification and adjusted to line up at an artificial infinity.*

 

*The Hexar RF and Fuji GSW690III service manuals have some useful information on adjusting a similar RF that shed some light on the subject. Both involve setting at infinity and then checking focus at 1m. You then tweak the infinity setting until it lines up *and* the 1m setting lines up. Then, and only then, if you can't get 1m to line up, you monkey around with the rate setting. Interestingly, the Hexar RF manual also references a "standard lens," which I imagine is something similar.

The standard lens technique - almost purely mechanical - seems to assume that the lenses the user owns are within tolerance for the RF cam, are correctly collimated, and will not exhibit any strange behavior depending on distance, aperture, etc.

 

I think the issue becomes an optical one when you get to huge clear apertures, focus shifts with aperture changes, and lenses whose focal lengths are not perfectly accounted by the design or build of the focusing helicoid.

 

Dante

 

I agree that the mechanical rangefinder technology is creaking with the dual demands of digital and longer and faster lenses.

 

The only way to ensure lens interchangeability is to calibrate cameras and lenses against independent standards, not against each other. Adjusting the camera to work with one particular lens runs the risk of problems with others.

 

For the camera, using the lens flange as a reference point, there's a defined relationship between the position of the roller and the distance at which the rangefinder image is then coincident. It would be very interesting to measure this over a number of cameras to see what sort of spread there is across unadjusted cameras.

[Guest guy_mancuso]

Dante when i was in Germany at the Solms plant . They mentioned the best lenses to test the RF where the 75mm and 90 mm lenses because of the tight tolerence with them. If you get them good usually the rest of the line will follow. For me to get everything good again is i had a M8 that just came back from calibration and tested all my glass and my 50 lux and 135 where off, so I sent them in for shims and I am dead on now through all nine lenses on both M8's.

[Guest tummydoc]

In theory any M lens when set at infinity should cause the coincidence of images of an object at infinity (that being something perhaps a kilometre or more distant, not the flagpole on the courthouse down the street); and in theory if none of the other adjustment points on the rangefinder are out of factory specifications the cam shaping of all other lenses should provide the necessary compensation to assure their proper focus. If you can't achieve repeatable infinity alignment with every lens, and or in spite of infinity alignment you are getting improper focus with some or all lenses at some or all distances, then you have a problem with other of the rangefinder's adjustments, or the individual lenses, or both, or your eyesight and the effective baselength aren't up to the task (specifically, lenses like the 75 Summilux and 50 Noctilux). That's it in a nutshell, no need for a doctoral thesis on the subject.

[Guest guy_mancuso]

Vinay , Leica did mention to focus on a star at night for infinity. Guess there not kidding about what is infinity

[Jamie Roberts]

My experience is the same as Guy's. I adjusted infinity focus for my 35 lux, 50 lux and a 90; my 75 Lux was then front focussing. The adjustment took about 3 hours.

 

Rather than mess with the M8, I took the lens in to Kindermann Canada, and bingo--it could not acheive infinity focus on their test bench. One lens--not RF--adjustment later, and they all work very well indeed.

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Hallo,

Look here: Leica M

[Guest tummydoc]

Vinay , Leica did mention to focus on a star at night

 

Just be careful which one you pick. Some of them have mean bodyguards:D