Does the Monochrom M246 have a different register from the M240?

[dante]

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So I was testing an Amedeo Contax adapter and an Opton Sonnar 50/1.5 with my M240, and it was showing the usual Sonnar behavior: focusing in front of the subject slightly (maybe 4cm) at f/1.5 and 1m and having the RF spot move past the infinity point (where it did line up at infinity, focus was correct).

 

The same lens and adapter mounted on my M246 shows perfect RF alignment at infinity and pretty much perfect focus at f/1.5. In fact, if you focused the lens slightly farther than the RF indicated, the sharpness would drop off, rather than picking up.

 

Is the actual flange-to-sensor distance in these cameras different? That would square with my suspicion that from M8 to M9, the distance increased - because the M8 back-focused all the time (with a lot of Leica and other lenses) and I've never seen that behavior since - even with fast lenses that had never been serviced.

 

I would have chalked this up to different interactions with different RF cams on two cameras, but that part is identical - and the difference in infinity focus (at the stop, not as indicated by the RF) is definitely there.

 

Dante

[fiftyonepointsix]

I've noted similar behavior between my M8, M Monochrom, and M9. M8 back-focus; M Monochrom almost perfect; M9 slight front-focus. NOT A LOT!, well within the specs of the lens. For example: the 5cm F1.5 Summarit is perfect at F1.5 on the M8, will front-focus on the M9 until F2.8 or so. It will drive you nuts, I just remember which lenses are best on what camera at a given F-Stop...

 

I've adjusted a lot of lenses for other people, and found it best to use my M9 when adjusting for another M9, M Monochrom for another M Monochrom. I think it has more to do with assumptions made for general field flatness across the size of the sensor in case of the M8/M9, and Chromatic Aberration for the M9/M Monochrom. 

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[thighslapper]

As we are dealing with mechanical parts with a accuracy tolerance rather than a fixed exact point and optics where the acceptably in focus range at different distances and apertures varies,  there is a whole range of variables which on some occasions cancel each other out and give you the happy with situation with your 50/1.5 + 246 and a different result with your M240. Add in complex lenses with floating elements and you will add another variable that may help or confound, depending on circumstances.

 

If you have 4 well calibrated M bodies (which I have) ...... and a dozen or so lenses which are also allegedly calibrated to Leicas tolerances you will still find some lenses with some bodies will have issues wide open and at various distances ...... not enough to be a problem with everyday photography ..... but certainly obvious if you test carefully. 

 

Even with Leicas rigorous attention to detail the unforgiving nature of digital sensors combined with the mechanical optics and focussing of a rangefinder makes 100% accuracy with every combination of components impossible.

 

....... and almost certainly the driving force behind a possible digital RF focussing mechanism discussed elsewhere in this forum. 

[fiftyonepointsix]

I've adjusted over 200 Jupiter-3 lenses and converted 50+ Sonnars to Leica mount for other photographers. I use my cameras to adjust them for use on their cameras. I noticed my M9 matched up lenses for their M9, and my M Monochrom matched up lenses for their M monochrom. I had a couple returned when using my M9 to set a lens used for their M Monochrom. Getting closer than that, I need the camera that it will be used on: but so far, has been unnecessary. 

 

I "Rationalize" this thinking the M9 is a color camera, no need to compensate for focus shift due to chromatic aberration. For the M Monochrom, the assumption would be to use a Yellow filter- which will cause a slight focus shift to infinity with most lenses. That means the RF calibration needs to take in an additional factor. Mirrorless technology would make all of this unnecessary. That would take all the fun out of it.

Edited August 29, 2015 by fiftyonepointsix

[gpwhite]

I've adjusted over 200 Jupiter-3 lenses and converted 50+ Sonnars to Leica mount for other photographers. I use my cameras to adjust them for use on their cameras. I noticed my M9 matched up lenses for their M9, and my M Monochrom matched up lenses for their M monochrom. I had a couple returned when using my M9 to set a lens used for their M Monochrom. Getting closer than that, I need the camera that it will be used on: but so far, has been unnecessary. 

 

I "Rationalize" this thinking the M9 is a color camera, no need to compensate for focus shift due to chromatic aberration. For the M Monochrom, the assumption would be to use a Yellow filter- which will cause a slight focus shift to infinity with most lenses. That means the RF calibration needs to take in an additional factor. Mirrorless technology would make all of this unnecessary. That would take all the fun out of it.

 

Very interesting and helpful information, 51.6!

 

I think we all experience that some M lenses work even better with the Monochrom than with the M, which I had presumed was an indication of the different sensors+firmware between bodies. For example, my 50 Summilux ASPH.

 

After reading one of Sean Reid's articles about filters on an M246, I tried a B+W Y52 and was stunned by the degradation of sharpness in the focus plane using three otherwise superb lenses (24 Elmarit, 28 Summilux, 50 Summilux). You seem to have explained it!

[120]

The distance is given in the service manuals. Why would Leica base a new distance on a particular filter?...Then the distance will be wrong for every camera and lens without the filter.

[fiftyonepointsix]

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As stated- I am "rationalizing this" after noting that my M9 agrees with many other M9's; my M Monochrom agrees with several other M Monochrom's, and my M9 and M Monochrom disagree with each other when used with the same lens and same filter. Put a Y52 filter on the lens, then the M9 and M Monochrom agree.

 

I don't know all of the assumptions made for exact calibration of the various Leica cameras, but adjust enough lenses and note a "pattern"- there has to be a reason for it. Use of yellow, orange, and red filters will shift focus towards infinity with most lenses. This fact can be compensated for in the calibration of the rangefinder.

[250swb]

This is all rubbish, Leica do not change the register distance from model to model, it would not only cause a justifiable uproar but be fundamentally against the ethos of the whole M system. Any variance is down to user error or lens and individual body error.

 

Steve

[fiftyonepointsix]

The register distance does not need to change, just the specific calibration of the rangefinder on various models. 

 

If chromatic aberration, spherical aberration, and field curvature did not exist- things would be much easier to calibrate a rangefinder camera.

 

When you have focus shift due to the above reasons, you can adjust the rangefinder to minimize the error based on assumptions of F-Stop used with a lens and in the case of a monochrome camera, what filter is used with the lens. The focus shift due to chromatic aberration in most lenses exceeds the classic 0.02mm calibration standard. Blue-Red shift of the type 3 50/2 Summicron is 0.08mm. F2~F8 focus shift due to spherical aberration is 0.05mm. Both numbers far exceed the calibration standard of the RF, so you need to make assumptions of how the lens will be used.

 

Adjust over 250 lenses for many other Leica users, note a pattern, take that into account when adjusting lenses for specific models of cameras- get less lenses sent back.

Edited August 30, 2015 by fiftyonepointsix

[250swb]

sorry, misread post

 

Steve

Edited August 30, 2015 by 250swb

[120]

I've noted similar behavior between my M8, M Monochrom, and M9. M8 back-focus; M Monochrom almost perfect; M9 slight front-focus. NOT A LOT!, well within the specs of the lens. For example: the 5cm F1.5 Summarit is perfect at F1.5 on the M8, will front-focus on the M9 until F2.8 or so. It will drive you nuts, I just remember which lenses are best on what camera at a given F-Stop...

 

I've adjusted a lot of lenses for other people, and found it best to use my M9 when adjusting for another M9, M Monochrom for another M Monochrom. I think it has more to do with assumptions made for general field flatness across the size of the sensor in case of the M8/M9, and Chromatic Aberration for the M9/M Monochrom. 

You have three bodies, none of which agree, so by definition you have at least two cameras out of adjustment. Since you are in the business of adjusting lenses, it would seem a better idea to pick one body and make a best effort that it agrees with a Leica service dept. The lens should be a black box--you adjust the lens to be exact at a particular aperture and subject distance, and it is or it isn't exact. The black box accounts for any aberrations affecting focusing. 

[fiftyonepointsix]

You have three bodies, none of which agree, so by definition you have at least two cameras out of adjustment. Since you are in the business of adjusting lenses, it would seem a better idea to pick one body and make a best effort that it agrees with a Leica service dept. The lens should be a black box--you adjust the lens to be exact at a particular aperture and subject distance, and it is or it isn't exact. The black box accounts for any aberrations affecting focusing. 

Not true. My M9 agrees with multiple other M9's, I use mine to set lenses for other people's cameras; and my M Monochrom agrees with multiple other M Monochrom's.

 

I have three cameras that appear to make different assumptions of lens behavior on the type of body: full-frame color; full-frame monochrome; and crop-frame color. This is similar to film days when many companies made lenses and cameras to the Leica 39mm screw mount standard: each made assumptions about how film would lay in their camera. It did not sit perfectly flat, and various bodies had different parameters to account for. As stated, this is observed behavior of lenses that I calibrated on my cameras being used on other people's cameras.

 

Nikon must have assumed their lenses would be used on a Leica M9...

Edited August 30, 2015 by fiftyonepointsix

[120]

Not true. My M9 agrees with multiple other M9's, I use mine to set lenses for other people's cameras; and my M Monochrom agrees with multiple other M Monochrom's.

 

I have three cameras that appear to make different assumptions of lens behavior on the type of body: full-frame color; full-frame monochrome; and crop-frame color. This is similar to film days when many companies made lenses and cameras to the Leica 39mm screw mount standard: each made assumptions about how film would lay in their camera. It did not sit perfectly flat, and various bodies had different parameters to account for. As stated, this is observed behavior of lenses that I calibrated on my cameras being used on other people's cameras.

 

Nikon must have assumed their lenses would be used on a Leica M9...

I don't think that is very convincing about the M8, M9, and Mono without some written source. It should be possible for you to email Leica service about it. My M8 did not agree with my M9 either, and they both needed adjustment out of the box. I don't credit that to any advanced "biasing" of the rangefinder adjustment for M9s compared to M8s; I credit that to Leica being not very conscientious with rangefinder adjustment.

 

If your three cameras don't agree with each other why are you looking for some advanced technological explanation?

Edited August 31, 2015 by 120

[dante]

I'd wager there is nothing such as a "service manual" for any digital M because only 2 or 3 locations in the world service them, and HQ trains them specifically. Leica uses specialized test fixtures to assess focus (and has for quite some time - DAG has one of the film ones). These are carefully controlled, proprietary, and expensive as hell. They do not have guys looking in a book for a number and using plunge micrometers to measure the four corners of the film plane. That introduces too much human error.

 

Dante

[120]

The film test fixture has its own part number and is described in every service manual. Why don't you just call or write Leica service for the register distance; I would be interested in what you find out...

[120]

I'd wager there is nothing such as a "service manual" for any digital M because only 2 or 3 locations in the world service them, and HQ trains them specifically. Leica uses specialized test fixtures to assess focus (and has for quite some time - DAG has one of the film ones). These are carefully controlled, proprietary, and expensive as hell. They do not have guys looking in a book for a number and using plunge micrometers to measure the four corners of the film plane. That introduces too much human error.

 

Dante

...begs the question, if you have a plunge micrometer how come you don't already have your answer?

Edited August 31, 2015 by 120

[jaapv]

It is also about sensor alignment and as far as I know Leica does not use mechanical measurements.

[120]

Do you think they changed the flange-sensor distance Jaap?

[luigi bertolotti]

In nominal terms, the flange/sensor distance has NEVER changed from M8, and in turn M8 sensor/flange distance is the same as the film/flange distance of all M Leicas  from M3 onwards (including CL), which in turn is 1 mm less than the film flange distance of all Leicas from Standard onwards.

 

Then lot of considerations on tolerancing do enter, very different from mechanical to digital Leicas, in which you have a sensor assembly to mount, and a sensor' surface which is covered by glass layers of different size in the different digital Ms... then a rangefinder (with its own tolerancing) and finally the beholder eye... .  I doubt that any discussion on this topic can bring to a definitive conclusion : it's a matter followed with high attention at Leica, with surely many compromises carefully balanced between the basic concept of backward compatibility and the needs (and possibilities) of the evolution of the technologies they do implement. 

 

What is sure (and the number of posts on this topic are a sign of this) is that current sensors and current lenses do approach the limits of the whole system... at film times none would discuss on such issue... if a Leica should had gone out of register (uneven, but did happen for heavy users) the fact emerged clearly, and it was easily adjusted by a good lab, period.

No surprise about the rumors on something new from Leica on the focusing environment...

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Hallo,

Look here: Leica M

[thighslapper]

I think some of you have a rather fanciful idea of what Leica do when they 'calibrate' things ...... ok, sensor alignment to the specified flange/sensor distance is done by laser with shims then added to the fixing mounts .......

 

...... but RF calibration was checked by a human looking at a series of sloping targets at various distances displayed on a video screen with a summicron 50/2 on the camera ....... and the distant target is (was) not at infinity ....... probably only 25m from the M9 assembly video. 

 

This process has apparently changed for the M240 ...... presumably as you have in-camera focus confirmation with focus-peeking ...... but even then it is not 'exact'.

 

If you want to use a mechanical RF coupled camera all the above issues are inescapable.