My used 35 lux is back focusing

[tashley]

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Hi Sergio!

 

I'm afraind I'm done messing with my RF - I tried this already but try as I might I could not get it to the point where it was slightly front focussing this one lens without messing the others up, and infinity. Actually, that's not quite true, I did shift the focus of this lens forward by a millimitre or two but that was the most I could achieve.

 

But in any event I think the exercise is rendundant because this focus shift is spherical in nature rather than linear: in other words the shift occurs at the centre of the field of view and not at the edges.

 

Still, the cron does it less than the lux did and I can live with it because of its many good qualities!

 

All the best

 

ps besides, the birdbox is now inhabited and I'm more excited to get shots of the little blighter leaving for work in the morning!

[charlesphoto99]

Sergio,

 

You don't even have to adjust the rangefinder to do this test - just set up at one meter at a flat object then smidge the focus to where it lays just in front. Then run through the apertures at that same focus setting. Mine backfocuses. Some may not. Affect may be more noticable at some distances than others. Not sure if I have a soft center or not, but it does begin to backfocus by an inch plus around f4.

 

I've said this several times on here, but please read carstenw's post (start's about replacing the red dot I believe) about the near/far adjustment and the infinity adjustment. In my foolishness I've adjusted both and can say it's a fine dance between the two. Adjusting the infinity only at nearest or farthest distance can leave you with focusing problems in the middle and/or the opposite end.

 

Okay, gott get some work done. Think I'm through worrying about this. Bottom line: some M8 rf's are coming out of the factory misaligned and the 35 summ asph backfocuses not at all for some and to a lesser/greater degree for other's. Ive seen lenses do this on other digital bodies so why not M8?

[ho_co]

Tim--

Thanks for trying the filter thing. I agree with your assessment that there is no focus difference at center. (My next suggestion would have been to try at the edges, but that has been obviated by the new Puts article on using the IR filters, and by Sergio's comments.)

 

I had also looked at the Italian shot when you first mentioned it and couldn't figure out the point of focus, but I had judged it adequate. Now Sergio finds it good enough to publish (quite a nice complement ), despite some sharpness problems.

 

Charles's comments are good: some do, some don't. I think that is now becoming clear. Jamie says he still wants to talk with Solms himself and try to get a more convincing answer. I think that's an excellent idea.

 

But in trying to answer a question of Jennifer Marroquin's in another thread, this question occurred to me: If there's a spherical aberration issue with some M lenses that causes them to have problems with a plane sensor but not with film, why wasn't there a similar outcry when the DMR came out? Could be a different design philosophy between M and R lenses, of course, but I doubt that. Could also just be a smaller number of DMRs sold, so a smaller circle of experience, but again I think that's questionable.

 

Thanks for the birdhouses and the filter trials and shots of LPs in their shucks; thanks the ridiculous amount of information turned up on this thread, as well as the tremendous amount of reason applied to what is apparently an insoluble problem.

 

"Some do, some don't."

 

--HC

[tashley]

Tim--

 

 

Thanks for the birdhouses and the filter trials and shots of LPs in their shucks; thanks the ridiculous amount of information turned up on this thread, as well as the tremendous amount of reason applied to what is apparently an insoluble problem.

 

"Some do, some don't."

 

--HC

 

 

And thank you for being a sane guide through a whacky jungle!

 

I think we've all kind of done this one to death now but it continues to interest me. The truth is out there but I wish we could get to it...

 

Best

 

Tim

[rosuna]

Zeiss has claimed that their lenses are designed to exhibit less focus shift than is usual, but part of the claim is based on a different location of the focal plane: a kind of average position so to speak. Not as good for best wide open performance, but better for stopped down performance. Leica has adopted the opposite approach: optimize for wide open performance and let the focus shift be compensated by depth of field.

 

http://www.imx.nl/photosite/leica/M8_8/m8_8.html

[sergiolov]

Testreports

 

Thanks for remembering us this article. Based on my tests, I perfectly agree.

Did the test again, this time at 1 meter,and not compensating for camera tilt, which brings the focus plane on the center of sharp area full open. From f2 to f8.

 

For Charlesphoto, I agree. The suggested (temporary) rangefinder adjustement was to permit a few real world shots.

 

Howard, as usual you are the reason between us.

 

Tim, well, these birds have theyr rights. Next birdbox test not before next winter.

 

Regards to all.

 

Sergio

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[ho_co]

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@Rubén--

Bravo for finding that citation (and listing its source!). I hadn't seen Puts's new article and am now "off to see the wizard."

 

I think that Puts said somewhere that Zeiss and Leica approach the location of the film plane differently, Leica expecting film to bow forward and Zeiss expecting it to bend backward. This quotation seems similar to what I think I saw, though I can't find that article now.

 

@Sergio--

Thanks again for another demonstrative set of tests; these were with the 35/1.4, right? There does seem to be a slight movement of sharpest focus with stopping down, but not enough to degrade the image in real-world shooting.

 

Still curious, though:

 

If this is a lens issue, why didn't we hear anything like this when the DMR appeared?

 

--HC

[Jamie Roberts]

{snipped}

@Sergio--

Thanks again for another demonstrative set of tests; these were with the 35/1.4, right? There does seem to be a slight movement of sharpest focus with stopping down, but not enough to degrade the image in real-world shooting.

 

Still curious, though:

 

If this is a lens issue, why didn't we hear anything like this when the DMR appeared?

 

--HC

 

IOW, the focus shift Sergio is showing (if it's not a shake) is nowhere near enough to account for several feet of on-axis error at f4.

 

As for the DMR, it's a completely different system with different glass to boot; there is no 35 ASPH R lens (I don't think my Summilux 35 is an ASPH design...).

 

I also think when people mess up focus on the DMR they blame themselves; in my experience it's easier to focus the M8 critically than the DMR, even with a magnifier and a better than stock DMR screen!

[ho_co]

Jamie--

You're right, the R lenses are different, but as you know, all lenses exhibit a certain amount of spherical aberration.

 

Since Leica is likely to have approached lens design for M and R the same way (for example, Puts speaks of "Leica lenses," not of an M design philosophy versus an R design philosophy), my question is simply this:

 

If we assume that some lenses work better with film than with flat sensors, as Tim has been told by Leica with other words, why are we discovering that fact for the first time with the M8, and why didn't we see it with the DMR?

 

Just that R users usually blame themselves first? Maybe so, but aren't they as picky about their equipment as M users?

 

I agree that most people find it easier to focus the M than the R, but I'm just fascinated that we're getting so many 'back-focus' threads with the M8.

 

--HC

[Jamie Roberts]

Howard,

 

I just deleted a very long post on the film plane / sensor plane stuff. Let's just say I need more convincing about lenses that work better with film (in some ways a much more variable focal plane) than they do with a predictably flat surface.

 

Leica saying that their lenses "are sharper" with film may have absolutely nothing to do with curvature of field or anything other than film's absolute (not practical) resolving power. Zeiss still makes all their resolution tests with film.

 

As for back-focus, I think it's becoming clear to some sales folks / camera folks I know that there are a number of M8s that come out of the factory backfocusing.

 

I have no idea why... but thankfully they can be adjusted and Leica is the company that will make it right, IMO.

 

As for the DMR, well, I did get my DMR focus adjusted from Kindermann Canada and Leica US (though it's because I dropped it off a tripod!!). When it came back, it did focus very well indeed

 

I think the whole film / sensor / lens design thing is mostly a red herring.

[wparsonsgisnet]

Tim, just for clarification,

 

When you focus at f1.4, and then stop down, do you refocus or are you depending on the focus setting from the wider opening?

[wattsy]

When you focus at f1.4, and then stop down, do you refocus or are you depending on the focus setting from the wider opening?

 

What difference would refocussing make in this case - i.e. when using a rangefinder camera?

[ho_co]

I appreciate your position, Jamie, and again I'm not about to argue. I'm not convinced either way and simply want to understand the issues better.

 

You'll notice that the question I raised ("Why wasn't this a topic with the DMR?") presupposes that you are correct and that both film and sensor focus the same.

 

An interesting two-part LuLa article starts at Digital Focusing Part One. I think some of what Ferguson says is obvious, but he demonstrates that depth of field doesn't behave the same way in digital as we are used to with film.

 

We know why--DoF wasn't 'real' anyway; we can now view images at 100% or larger; the flatter sensor doesn't smudge like film (see e.g. http://www.imx.nl/photosite/leica/M8_8/m8_8.html):

 

The main characteristic of the sensor surface is its absolutely flat surface: there is no depth like we have in film emulsions. Here we cannot count on emulsion thickness to compensate for mechanical errors in accuracy or focus shift.

Puts agrees that digital or analogue, focus is focus. But he says that spherical aberration is a real issue, and goes on:

 

Zeiss has claimed that their lenses are designed to exhibit less focus shift than is usual, but part of the claim is based on a different location of the focal plane: a kind of average position so to speak.

And:

 

The tolerance level in film based cameras is a few hundreds of a millimetre, in the M8 that level has been reduced to a few thousands of a millimetre.... This makes the M8 the most accurately machined and assembled M camera in history. This is done to compensate for the lack of image capture thickness.

So why are we getting so many reports of backfocus in the M8? A bad batch of lenses? Possible but not likely, because that would presuppose a single operator incorrectly assembling those affected.

 

Puts says that Leica lenses should be used near open aperture because they are designed that way. It's probable in my mind that we've simply (re-)discovered this fact with the M8 because of its flat sensor. The film compensates to a certain degree for the design of the lens, or to put it the other way, the lens was designed to maximize its performance with the media of the day.

 

With a digital sensor, maintaining that special "Leica something" may require more understanding on the users' end and also some design tweaking by Leica.

 

--HC

[Jamie Roberts]

Howard, not to put too fine a point on it, I believe there are some M8s--not lenses--that have their RF mis-adjusted at the factory.

 

Not on purpose; not by design Mistakes do happen... and when a whole lot of people complain about backfocus "all at once" then you know it's not rediscovering old lens designs are "faulty" (they're not, for the most part for the sensor resolution we're talking about--and no, we're not talking 1930s lens design here!).

 

No--Occams razor would say the simplest explanation is best: some new M8s need tweaking is all.

 

This happens with every other manufacturer of professional cameras; why Leica would be immune here is the question.

 

I'm also not sure Puts is right about the purpose of the higher tolerances in the M8; he implies they're there to compensate for lack of film emulsion depth or "fudge factor."

 

A more believable (simpler) explanation to me is that the camera sensor position, with the necessary microlensing to make this all work, is more susceptible to subtle misalignments at the edges of the frame!

 

So, again, to me we're hearing about a lot of backfocussing because--ay carumba!--some new M8s backfocus and need to be fixed. Nothing more complex than that.

[ho_co]

Jamie--

I was thinking of not responding because we're both close to agreeing (though with a slightly different slant) and close to beginning to repeat ourselves.

 

Agreed, if the reports we are hearing are accurate, a surprising number of M8s are shipping with improperly adjusted rangefinders. It would be interesting to follow that topic.

 

I'm afraid I don't understand your reference to "misalignments at the edge of the frame." Misalignment of the sensor, the microlenses, the lens flange, the lens?

 

I respect Mr Occam, but I don't think that the need for tweaking M8 bodies is a simpler solution than the one Puts puts forward.

 

You and I have a very narrow difference of opinion. We agree that something is off and that some M8s are appearing with improperly adjusted rangefinders. You feel that that is probably enough to explain the problems we're hearing of, and I feel there's likely more involved.

 

No biggie, just the necessary question, "Have we got to the bottom of this or not?"

 

I just hope Jennifer Marroquin gets her camera and lens working together. The rest of this will straighten itself out pretty quickly.

 

--HC

[tashley]

Tim, just for clarification,

 

When you focus at f1.4, and then stop down, do you refocus or are you depending on the focus setting from the wider opening?

 

 

As Wattsy says, there's no point in refocussing. Indeed it is vital NOT to, if the test is to represent a level playing field. So I focus as accurately I can for the first shot then make damned sure not to shift the focus one iota as I progressively stop down. And I use a tripod.

 

Best

 

T

[gravastar]

In the back of the March/April 4/2007 LFI there's a preview of the next edition's content ... guess what ....

 

"SHIFTING FOCUS - Since the introduction of the M8 wev'e been hearing about more and more cases of lenses suffering from focus shift when stopped down. Perhaps digital images push you to look closer than usual and discover the effects of spherical aberration. We explain the situation."

 

 

Bob.

[tashley]

Jamie--

I was thinking of not responding because we're both close to agreeing (though with a slightly different slant) and close to beginning to repeat ourselves.

 

Agreed, if the reports we are hearing are accurate, a surprising number of M8s are shipping with improperly adjusted rangefinders. It would be interesting to follow that topic.

 

I'm afraid I don't understand your reference to "misalignments at the edge of the frame." Misalignment of the sensor, the microlenses, the lens flange, the lens?

 

I respect Mr Occam, but I don't think that the need for tweaking M8 bodies is a simpler solution than the one Puts puts forward.

 

You and I have a very narrow difference of opinion. We agree that something is off and that some M8s are appearing with improperly adjusted rangefinders. You feel that that is probably enough to explain the problems we're hearing of, and I feel there's likely more involved.

 

No biggie, just the necessary question, "Have we got to the bottom of this or not?"

 

I just hope Jennifer Marroquin gets her camera and lens working together. The rest of this will straighten itself out pretty quickly.

 

--HC

 

Needless to say I remain 100% certain that, though there are certainly a number of M8s with out of whack RF out of the box, there is more to the issue with these 35s than just that. I am absolutely confident that the RFs on my first M8 is good (I haven't used the second one enough or with enough deifferent lenses to be certain of that one yet but I think it's fine.)

 

Jamie will no doubt continue to believe that my RF is not finely enough adjusted to ensure the point of focus is at the leading edge of the DOF. That may be true but I doubt it, since the 50Lux behaves perfectly throughout and has less DOF than the 35 luxes or crons.

 

I know that the reason we continue this debate is in the vague hope of uncovering some fact or factor we've all missed so far but for me, Mr. Occam should be applied as follows.

 

Backfocus can be created by the RF, the lens, or both. My RF is fine, my other lenses (and some have other issues) do not backfocus and I have had three Leica 35's that do, on every body they are tried on. Many other people report the same.

 

That tells me it's the lenses.

 

SO is it a 'common fault/manufacturing/QC defect' or a 'characteristic resulting from having been designed for film and arising from the necesarry compromises made in design'?

 

The manufacturer tells me categorically it is the latter. For me this is the simplest explanation: if Leica have tested my two Luxes and declared them normal but accepted that they backfocus, Mr Occam can take the rest of the day off: the answer is obvious.

 

There is another, closely related question: why are there clearly some versions of the lens around that appear to behave well? In particular Sergio and Jamie. Are their rangefinders miscalibrated, or have they managed to find a very small sweet spot where their individual lenses are up one end of the natural range of variance and their RFs at the other end? Is it because Jamie's is chrome? Etc etc.

 

In other words we now need to find out, not why mine is behaving as it does, which is 'normally' but what is special about the 'abnormal' ones?

 

So: Jamie and Sergio, tell us the exact spec of your lenses. Full lens name, year of manufacture, colour, etc etc.

 

I'm quite sure that if we all work together on this we can solve your problem!

 

:D

 

Tim

[Jamie Roberts]

Ah Tim--

 

First, I *don't* think your rangefinder is off anymore (though there may be a mount issue still)--you adjusted it and got better focus on your 50 1.4.

 

We don't disagree at all. We did till you adjusted the rangefinder: now it's lenses as you say.

 

So again--Mr Occam comes hasn't left the building--you believe that there's something systematically flawed with all recent 35s (at least on the M8). I believe (based on my experience and others) that there's something wrong with the lens samples you had.

 

To me, one is vastly more probable than the other Though again, I have every sympathy here. Actually, both could be right insofar as there may have been a run of 35s that are in fact, misaligned in some way.

 

Apart from all of that--there are some cameras, clearly, that backfocus from the factory--my own included. Once adjusted, all the lenses actually work as predicted.

 

Who has the problem again?

 

Oh yes--Jennifer. We all agree she should have the camera and lens looked at by someone who knows what they're doing, right?

 

@ Howard--yes, I'm not sure we even disagree, except on the whole media thing. Can't wait to read what LFI says about all this!

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[charlesphoto99]

Okay, we all have to remember that the lens and rangefinder are actually seperate things and can work independently of each other. With the magic of digital one can set the camera on a tripod and move it back and forth with the subject and find perfect focus no matter what the rangefinder says (one should be adjusting the rf to the lens, not the lens to the rf). Do that and then perform the backfocus test. My 35 backfocuses. My other lenses don't or at least not to the degree the 35 does. The 35 asph is so magic at wider aperures I hesitate to replace it. But I may try finding a late model pre-asph summicron.

 

Anyway, for me the rangefinder calibration is now a moot point as my body will be going back due to a discovered row of dead pixels at higher iso's. I will insist that Leica check the rangefinder before it leaves whether it's a repair or a replacement.

 

Looking forward to that LFI article.