Mount to sensor distance

[jrh68uk]

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Are there shims between lens mount and M body to fine-tune the distance between lens mount and sensor? Or does this type of adjustment require a re-shim of the sensor itself?

 

I've just reported a problem with my new M which (after laborious testing) I have concluded is down to the lens mount being a tiny bit too far from the sensor. The explanation I have sent to Solms/Wetzlar is long-winded and I shan't repeat it here - suffice to say that I've been able to show with image proofs that a lens at the infinity stop can't quite reach focus at distance as it did on my M9/M8 which I owned before the M. This is nothing to do with the rangefinder adjustment but the actual ability to reach focus at long distance. It's easily observable when comparing M to M9 files.

 

I guess I'd just like to think that they can whip off the mount, put in a slightly thinner shim than the one in there (if there is one) and send it back after the necessary RF calibration, rather than take the whole insides out and mess around with the sensor. In every other respect, the camera hardware is perfect. An easier fix would make me feel easier about sending it in

[colonel]

certainly no shims, just precision engineering

if it was out that would be a major production issue!

 

sounds like a lens issue. Have you taken it into a Leica shop for testing ?

[jaapv]

There are no shims. Mount-sensor distance is finetuned by the sensor. As that has a tolerance in thousandths rather than hundredth of a mm it must be done by Leica. One needs sophisticated laser equipment to check. Checking/adjusting the sensor is a routine operation at CS.

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I too would look for a lens problem rather than a camera one. Do send the lens with the camera.

[marknorton]

Indeed, the thinnest sensor shim I have seen is 0.01mm which corresponds to a setting accuracy of half that. By comparison, that accuracy is about 8 times the wavelength of light.

 

There is some evidence that, over time, the point in the CCD sensor package taken as reference has changed. The active part of the sensor is much thicker than film emulsion.

[wizard]

...The active part of the sensor is much thicker than film emulsion.

 

Much thicker? Up to now, my understanding was that the sensor plane used for adjustment purposes is much THINNER than a film emulsion, hence the greater precision required during adjustment.

 

Andy

[jrh68uk]

Hm, OK. My reasons for concluding a camera, rather than lens, problem is that it's evident that none of my lenses will *quite* attain sharp long distance focus any more, wide open. Well, those that stop at the infinity point, anyway (that's all but my 28 Elmarit ASPH). With wider lenses it's harder to detect/prove anyway, but my two 50s and 35 I see the issue. I noticed because of front focus and realised that (unlike with previous bodies) I got to the infinity stops but needed to go a tiny bit further - impossible, of course.

 

Everything was fine with the M9 and the M8 before it. Everything is fine with my current film bodies and these lenses. If I have all lenses adjusted to effectively move them closer to the sensor at their infinity stops (and yes, it will be a minuscule amount) it will cure the problem (at my cost!) for this M240, but what about any future digital bodies and my current film ones? I find it difficult to accept that my M9 and M8 could successfully record sharp long distance images with all my lenses wide open yet the M240 cannot and that this could be lens problems. But then, perhaps it is, and all of my lenses are out and so were my M9 and M8 even thought the M9 was calibrated again in Solms.

 

At least two lenses were calibrated in Solms to the M8/M9 standard, though, admittedly not the 50s. Now I'm not sure what to do, although what I do know is that my, say, 50 cron at f/2 was noticeably sharper at its infinity stop with distant objects on M9/8 than it is the same on the M240.

 

I guess I'm terrified of having my lenses altered when they have been fine up until now. I still think it's a camera thing but (thanks Jaap) your explanation proves that it's not as simple as a quick shim swap at the lens mount.

[marknorton]

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Depth of field works on both sides of the lens. For an object at a given distance, the image projected onto the sensor will be sharp over a given depth which is obviously tiny. It's easy to place film emulsion in the centre of that image depth but it's much more difficult for a digital sensor; where is the zone of optimum sharpness as perceived by the sensor?

 

A film M relied on a pressure plate to create a narrow channel through which the film passed but I have never seen shims to fine tune the film to lens mount distance. It just worked.

[jrh68uk]

There is some evidence that, over time, the point in the CCD sensor package taken as reference has changed.

 

If this is true then I suppose that could explain it. Perhaps my M240 is as it should be but my lenses, fine up until now, were on the outer limit of acceptance before this possible change of reference and are now just outside this limit.

 

I'd prefer the reference to be that of my M9/8 though

 

I still worry about altering lenses that have been fine up to now, though. Aside from the cost, I may find that my film bodies need to be re-adjusted and that any future digital M will mean sending the lot back in again.

[jrh68uk]

I guess I should ask whether anyone has ever had the sensor plane (of any digital M) altered to correct a perceived focus problem.

 

If not, and I am really barking up the wrong tree, then maybe I should bite the bullet and send at least my 50 cron, 50 lux ASPH and 35 cron ASPH in with the M. I'd have to hope that any changes to lenses won't be visible in a negative way on my film bodies and that any future M, if ever that comes my way, will be adjusted the same.

[jaapv]

As I said, it is pretty routine. I have had cameras in for other things and often the work slip would say “adjust sensor” without me specifying a problem. No, adjusting to the newest standard will not impact the performance on film, if anything it will be improved .

[jrh68uk]

Thanks Jaap - that's reassuring.

 

I've suggested to CS, whose initial response was as prompt as ever, that I perhaps send my two 50s and 35, at least, in with the camera. They can decide which one(s) need adjustment, all in one go, if they agree. I know what I've seen after (too much!) testing but I'm not qualified to make a diagnosis when it may all be down to opposing edges of tolerance or something like that.

 

Hopefully, I'll end up with a system even better than before.

[Maarten]

Hi Jason, if I may say so: you think a little too much.

You are not happy with the performance of your M-body and the lenses you have. That feeling will not go away.

The only remedy is sending the camera with one or two lenses to Germany. Leica Wetzlar (!) will make it work and they won't adjust your lenses to a faulty body.

Don't start thinking how a CS guy will pull the leather from your body to slowly work his way into your impeccable Leica.

CS adjusted the sensor of my M8 and I couldn't be happier when suddenly all my lenses (including a Tele-Elmar 135mm) focused perfectly.

My camera looked exactly the same when I got it back, it just worked better.

I advice you to chose the same solution and have your camera fixed so you can start to really enjoy it instead of thinking what could be wrong with it.

Maarten

[jaapv]

Stop worrying my friend. These are the people that designed and built your babies in the first place. Sure, they are human and sh!t happens, but over 99% goes perfectly ( and 1% invariably ends up on this forum…) I always got my gear back from CS better than new. Call Solms and ask for Andrea for your peace of mind. I once needed to send her a huge bunch of flowers for the way my problem had been handled, and could have done so many a time more.

[jrh68uk]

Maarten, Jaap, you're both right, of course. I think I allowed myself to become a little too obsessed with testing, trying to convince myself that the problem may be one I should accept otherwise I risk upsetting the system (the system being all four of my current bodies and any potential future ones, and all lenses working together). But of course, it's an issue I couldn't comfortably accept.

 

The wonderful Andrea is on the case and I'm sending in my three "longest" lenses together with the M. Now that that's happening I feel a huge sense of relief! Silly really.

 

Thanks for your words of wisdom.

[pico]

I thought I saw sensor shims in the video of making a Leica.

[hoppyman]

I don't understand why the RF adjustment is not being considered?

I think that the purpose of having multiple shim points is to also fine tune flatness within the lens register. They need not be and probably aren't all shimmed equally unless you had a mythically perfect assembly.

[jrh68uk]

Just to tie this up, and maybe counterbalance another thread going on currently about dreadful QA...

 

My M240 and 3 lenses (50 'lux ASPH, 50 'cron, 35 'cron ASPH) have just returned from Wetzlar. I don't actually think much was done to the camera, as far as I can tell, but all three lenses have been adjusted. Both 'crons also had their mounts repaired because, apparently, there was a bit of play in them. I hadn't noticed.

 

Everything is spot-on. I mean, absolutely bang on the mark. I can't fault it. The two 'crons have slightly stiffer focus action, which is fine and must be a good thing.

 

In addition, Leica CS (mainly Andrea) have been superb, especially considering that I may have been high maintenance at times. I was without these for a month, which is better than I was expecting. It was a long month, but that's all it was.

 

One very positive survey form will be winging its way over to Wetzlar...

[250swb]

 

I find it difficult to accept that my M9 and M8 could successfully record sharp long distance images with all my lenses wide open yet the M240 cannot and that this could be lens problems.

 

It is difficult to tell from your description the amount of unsharpness you are experiencing, but the M240 does need more sharpening in post processing because of the higher pixel density. So if you are judging based on a comparison between unsharpened M and M9 files there could be a significant difference visually, but not in actual terms when the image is sharpened. Just a thought.

 

Steve

[wlaidlaw]

The problem with older M’s is how much film “bow” do you allow for? Were the lenses designed to compensate for curved film? In the latter years of Contax, Zeiss was obsessed with film flatness. This is one reason they almost universally used motor advance, where the cassette side was braked at the end of the wind, to maintain film tension. On their more expensive SLR’s, they had a ceramic pressure plate with tiny holes, through which a vacuum was applied to hold the film flat against it, just prior to the shutter firing.

 

Wilson

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Hallo,

Look here: Leica M

[jrh68uk]

@Steve, yes, I can't really describe in words although I did provide files as part of the problem description to Leica. Whether or not they examined them, I don't know, but they have checked the camera over and decided that it's the lenses that needed adjustment rather than the sensor shimming. Digitally, everything is perfect and I have to trust the experts that they made the right decision as to what to adjust.

 

If I'm honest I'm wondering about results using my film bodies now, but I probably don't need to.