Trying to understand rangefinder misalignment

[chris_tribble]

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One of my M9 bodies is going to need a little TLC as the rangefinder no longer fully reconciles the focusing patch at infinity - not a big deal and happy to put it into Solms for a spring clean while it's still in warranty!

 

Reason for writing is I'd be interested in understanding how I'm still able to focus accurately on close and distant objects while the rangefinder itself is off... Grateful for any clarification on the mechanics. Many thanks for any enlightenment you can offer...

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[jaapv]

Chris, the RF adjustment is mainly on two points (there is a third for middle distance, but let's not visit that one again;)) Closeup and infinity. Closeup is most critical and easily noticed, but the infinity focussing in the RF will show up at the smallest twist of the focusing ring. Even if it is off minimally, as long as the lens focuses to infinity you wouldn't notice. So in your case it is probably just the infinity linkage that is slightly off. That means that if you were to correct it by the Allen key method, you would most likely throw close focus out. In other words: It is a logarithmic scale, just look at the distance markings on you lens.

[lars_bergquist]

Amongst lens designers, the distance to 'infinity' is usually taken to be 1000x the focal length. So with a 50mm lens, it is just 50 meters away. Some people can cover that distance in five seconds, on foot and from standing. Everything further away than that is simply depth of field, which will adequately cover the rest of the visible universe. So even though your rangefider can discriminate between subject distances beyond the 'infinity' of your lens, your sensor probably can't.

 

The ultimate range of the M rangefinder itself seems to be something like 170m.

 

The old man from the Age of the Tape Measure

[jplomley]

Chris, did the rangefinder you are sending in ever focus properly at infinity, or have you only just noticed this now? The reason i ask is that I'm seeing more and more reports of M9s which were working properly, and than for whatever reason, their calibration starts to drift.

[diogenis]

Considering Lar's excellent reply, you can now understand what precision is for Leica lenses, and how difficult it is for Leica to produce lenses that coincide with most M cameras RF. Because lenses do have various focal lengths and because obviously, the mechanical cam (link) of the RF patch is fixed, it only leaves that bronze driver to actually drive the RF and drive it accurately. Meaning when in infinity of a particular lens, the lever stops. When my camera's RF was a bit misaligned, it did overshot my 50lux about a millimeter. After a visit to Solms, it was calibrated back to full precision, without the 50lux ever visiting the factory! I can only imagine how strict those tolerances are

[chris_tribble]

Chris, did the rangefinder you are sending in ever focus properly at infinity, or have you only just noticed this now? The reason i ask is that I'm seeing more and more reports of M9s which were working properly, and than for whatever reason, their calibration starts to drift.

 

Jeff - to the best of my knowledge it was fine until a recent trip where it got used a lot and it and I got bumped around on some fairly primitive transport... I've compared 28 / 35 / 50/ and 90 lenses on the problem one and a second (earlier) M9 and it definitely seems to be only an issue on the one body (and not lens related ...).

 

Lars - thanks for the explanation

 

Jaap - I wasn't planning to use the allen key this time...

 

Best..

[Guest trond]

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Dear Chris,

 

I have had my share of problems with focus calibration on M lenses and M9.

 

In my case the M9 was spot on, but two of my 10 leica lenses where quite a bit off.

 

These two lenses, less than one year old, a 35 lux and a 21 lux, both had two trips to Solms.

 

The 35 lux was dead on after Solms did their second attempt.

 

On the first try both lenses came back worse than when I sent them in.

 

The 21 lux is still in Solms and has stayed there for seven weeks now!

 

I refused to send inn my M9, even if Leica wanted it in, as I was sure that it was accurate, and would not risk that they "fixed" it, so that the rest of the lenses also had to be sent in!

 

Further my two 50 Luxes, ASPH and non-ASPH, 50 Cron ASPH and non ASPH and a 90 APO-Cron, where all spot on at 1 meter and at infinity.

 

The lens problem was further reaffirmed by testing the 35 and 21 luxes on two other M9s, with the same result.

 

This is apparently a big challenge for Leica, and the all famous, Mr Erwin Puts, explains this in a very nice way in his analysis of range finder accuracy in this thread:

 

rangefinder issues

 

Best regards

 

Trond

[perb]

Reason for writing is I'd be interested in understanding how I'm still able to focus accurately on close and distant objects while the rangefinder itself is off... Grateful for any clarification on the mechanics. Many thanks for any enlightenment you can offer...

 

Here are some links I collected from the forum:

 

http://www.l-camera-forum.com/leica-forum/leica-m9-forum/122176-m9-coincidence-infinity.html

 

http://www.l-camera-forum.com/leica-forum/leica-m9-forum/121373-factory-m9-lens-rangefinder-focus-tolerances.html

 

In this last one pay extra attention to the explanations by Julian Thompson. It's a long thread, so browse around. I think you will find it interesting:

 

http://www.l-camera-forum.com/leica-forum/leica-m9-forum/115034-rangefinderproblems-new-m9s-2.html#post1223116

 

Regards

Per

 

PS. Chris, I can see you followed the last of my three threads, so browsing through it should bring back memories

[Guest mc_k]

...

Reason for writing is I'd be interested in understanding how I'm still able to focus accurately on close and distant objects while the rangefinder itself is off... Grateful for any clarification on the mechanics. Many thanks for any enlightenment you can offer...

 

There was another thread on this a while back. It is hard to compensate even when your camera is not off by much. One suggestion was to use the difference between the two images in the finder, instead of the focus ring, to compensate.

 

You can also use the lips or ears in lieu of the eyes to compensate a portrait. If your camera front-focuses you can use the reframing error to compensate. You can zone focus. These three work o.k. in my experience.

 

If your camera is off by a lot, I guess you can compensate with the scale.

[Guest mc_k]

...It is a logarithmic scale, just look at the distance markings on you lens.

 

Can you elaborate on this please, why logarithmic--what is the function linking the engraved scale to the object distances??

 

thanks

[doug_m]

Okay so what about when its the lens that is off at infinity? Lars and Jaap- and others- can you explain what is going on with my 50 lux ASPH:

 

It focuses fine up close but at "faraway" infinity- let's say a kilometer or more away- there is a double pole when I focus on a light pole on a bridge (for example). At 0.5 km "infinity" seems to be spot on (no double pole). The "faraway" infinity image itself seems to be just fine when I zoom in on the LCD screen. The rangefinder seems to not go quite far enough resulting in the "double pole" effect- rather than overshooting.

 

This problem does not exist with numerous other lenses including a 75mm and 90mm lens. I also get essentially the same results with the M8.2 as I do with the M9- in every respect and with various lenses.

 

I think (and hope) this is more of an annoyance rather than a problem that results in poor IQ. What do the experts on the forum think? Thanks.

[lars_bergquist]

I would say that the focusing cam movement of the particular lens is not quite up to snuff. This is a matter for the people in Solms, I'd say -- I don't think even an authorized repair shop can do anything.

 

I wonder if even Solms can rectify the problem, other than by exchanging the lens.

 

The old man from the Age of Eyeball Focusing

[pop]

Can you elaborate on this please, why logarithmic--what is the function linking the engraved scale to the object distances??

 

thanks

 

Similarly to curved mirrors, thin lenses follow a simple equation that determines the location of the images given a particular focal length (f) and object distance (S1):

where S2 is the distance associated with the image and is considered by convention to be negative if on the same side of the lens as the object and positive if on the opposite side of the lens.[38] The focal length f is considered negative for concave lenses.

 

source: Optics - Wikipedia, the free encyclopedia

 

The old man from the Age of Eyeball Focusing

 

Ha - in those days my eyes still used to focus, too.

[Guest mc_k]

Thanks for the reply, Philipp. I think you are right, I suppose you get the distance the lens moves forward from the lens equation...the function is not logarithmic...and I suppose you get the engravings in another step, from the pitch of the focusing thread.

 

But I am only guessing, so I will ask Jaap again for a source, or an explanation why the scale you end up with is logarithmic.

[pop]

... why the scale you end up with is logarithmic.

 

I don't think it is logarithmic. It certainly is not linear. I think it is hyperbolic, and that would be in keeping with the law of optics.

 

As a quick and dirty measure, I wrapped a ruler around the barrel of the first lens that came to hand and measured the distance between the engraving for different distances and infinity. This is what I came up with:

 

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Both axes are measured in cm. hence, the engraving for a distance of 8m is roughly half a centimeter before the engraving for infinity.

[Julian Thompson]

Indeed, doug, if your other lenses allow the vertical poles to line up at infinity then the lens ramp is not right on your 50 lux.

 

After much argument and discussion, plus much work, put simply, the adjustment of the rangefinder is a simple four step process -

 

One, ensure the roller is being presented to the lens cam in a perfectly perpendicular fashion. This is unlikely to need adjustment but if it does then there exists a bending tool which must be used on the arm with the roller on it to correct the setting.

 

Two, set the infinity adjustment using the allen key in the roller cam until infinity vertical poles line up perfectly.

 

Three, adjust the LENGTH of the arm itself by loosening the slot head screw and carefully moving the cam to alter the total throw of the rangefinder arm to achieve close focus perfection. This is a fine adjustment.

 

Four, re-correct infinity to compensate for the adjustment at 3 above that will inherently slightly move the roller in relation to the lens barrel.

 

Recheck and confirm. That's really it.

[Guest mc_k]

...

 

Elegant answer! Thank you for the graph.

[Nicoleica]

Indeed, doug, if your other lenses allow the vertical poles to line up at infinity then the lens ramp is not right on your 50 lux.

 

After much argument and discussion, plus much work, put simply, the adjustment of the rangefinder is a simple four step process -

 

One, ensure the roller is being presented to the lens cam in a perfectly perpendicular fashion. This is unlikely to need adjustment but if it does then there exists a bending tool which must be used on the arm with the roller on it to correct the setting.

 

Two, set the infinity adjustment using the allen key in the roller cam until infinity vertical poles line up perfectly.

 

Three, adjust the LENGTH of the arm itself by loosening the slot head screw and carefully moving the cam to alter the total throw of the rangefinder arm to achieve close focus perfection. This is a fine adjustment.

 

Four, re-correct infinity to compensate for the adjustment at 3 above that will inherently slightly move the roller in relation to the lens barrel.

 

Recheck and confirm. That's really it.

 

And then, send your camera and your holiday fund to Leica in order to have the rangefinder readjusted so that it works again.

Seriously though, although the basic adjustments are quite simple processes. If you try to do this without the correct test jig, and technical proficiency in such adjustments, you stand a very good chance of mucking it up completely.

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[Julian Thompson]

And then, send your camera and your holiday fund to Leica in order to have the rangefinder readjusted so that it works again.

Seriously though, although the basic adjustments are quite simple processes. If you try to do this without the correct test jig, and technical proficiency in such adjustments, you stand a very good chance of mucking it up completely.

 

Honestly that's not true. It's very easy. If you can look at a photo and say with certainty that 'Yep, that's in focus' - then you can do it.

 

Anyway - over and out from me. I can adjust my rangefinder and bully for me but my energy for educating others and furthering my own knowledge on the subject is at an end.

 

I'm off to take some pictures with my new M7!

[Photoskeptic]

Over on this side of the pond we don't "muck" with anything. We do however use a word that has the last three letters of muck in it

I used my M8 with the rangefinder misaligned at infinity for three years! I was too scared to send it to Leica after all the horror stories. I never ended up with an oof shot. This might be due to an apprenticeship which featured three Leica film M's first. When I decided to sell the body I sent it to DAG. The price was twice as much as he told me on the phone and the time he had my body was twice as long as he promised, however he did an outstanding job and when I popped a lens on and tested it I said to myself, "so that's what I've been missing".

Now I'm pining for an M9 but am hearing all sorts of horror stories about back-focusing. But who cares? You can't find one for sale anyway.