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Backfocusing lenses. Is it a Leica-only disease ?

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Up until now, I thought that backfocusing lenses was a kind of "bad luck" only occuring to others but, after receiving my 90 Elmarit back from Solms after coding and cleaning, I decided to take the test (the lens came back with the front part loose i.e. it unscrews as soon as you move the f ring). And bingo ! I am a full member of the community now. Not only the 90 was way out but also my Nocti and my 135 Apo. Only the 35 lux and the 75 lux were spot on. O.K., I'll do what all of you did, send them to Solms for adjustment but with the kind of QC they perform, I really wonder !?

Now, on a more general level, why does this backfocusing problem happen only to Leica lenses ? I have never seen in this forum anybody reporting this problem with a CV or Zeiss lens ? Or am I wrong ? I would rather prefer to be wrong.....

 

Michel

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No, it's a lens disease. You get this in SLR lenses too – the focus can often shift a bit when you stop down, and the pitch of the essentially linear focusing helical is really a compromise. The reason for the shift, I understand, is an effect of spherical aberration, and it is of course more noticeable in very fast lenses.

 

The old man from the Age of the Box Camera

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Not sure if it's Leica only disease but I have one Leica Lens that does it, a new 75 Cron ASPH.

I first noticed it on the 4th when I was taking smoe shots of a orchestra playing at a out door fest in my town. I know I was focusing on the face of one musician and the guy behind him was in focus when I looked the shots on the computer that evening. It also changes with the distance you are focusing. At close range it's only off a little bit. At longer distances the backfocus grows.

 

Also I sent this lens in to NJ to have the aperture ring tightened and when I got it back the front of the lens unscrewed when I was taking a filter off of it.

I'm going to send it in again.

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In testing for my 35 mm lens review, I found that the Zeiss 35 Biogon also slightly shifts focus as well as it is stopped down. Focus shift, of course, is different from back focus.

 

The CV 40/1.4 Nokton also shows some focus shift, as does the 35/1.4 Aspherical and 35/2.0 Aspherical.

 

Cheers,

 

Sean

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Lars,

I tend to agree with you about the "off-focus" (back or front) being more problematic with higher speed lenses, yet I empathize with Michel's omments. The only lens that I have any focus issues with is my Leica 75/2. All of my Zeiss and CV lenses are spot on in focus, regarless of aperture stopping down, or distance to subject, and that includes fast CV Nokton lenses (35/1.2 and 50/1.5) and a Zeiss 25/2.8. When I focus on something with the rangefinder, that is what is in focus in the capture. If I change the aperture (stop down), I still have the same plane of focus as before, but now with a greater DOF.

 

I have learned how to compensate shooting with the Leica 75/2, and I expect to due the same with the coming Noctilux. Understand the reasons posited by Leica (and some others) about setting the focus points at close distance, and the blue/red wavelength separation concept, but the bottom line, for me, still seems to be that other lenses do not seem to have the same focus issues as the much more "refined" and optically outstanding Leica lenses. BTW, both of my CV Noktons are asphericals also, and they do not suffer the back-focus issues that the 75 Cron does, near or far, at any aperture.

 

Not trying to foment a long standing debate, but Michel raises the issue of QC at Leica and other lens things, and personally, I am not impressed, based on the growing list of stories presented here. I have not personally experinced any issues on lense adjustments from Solms, because I have not sent one in, and unless the Noctilux is way out of whack, probably will not.

 

So, your comment about it being a lens disease seems to apply more to just Leica, from my experience. None of my older fast Nikon lenses from my filme days, nor any of my fast Canon lenses that I use regularly have any of the back/frontfocus issues reported for Leica lenses. I am sure there are probably some very minor off-focus issues, but nothing even close to what I see with my 75 Cron.

 

Just my perspective here. I love the Leica optics for sharpness, clarity, differnt contrrasts, bokeh, etc., but I am a lot less impressed with the seemingly quite prevalent off-focus issues that are being reported. My CV and Zeiss glass seem to be head and shoulders above the Leica glass for being more spot on in focus, and then keeping that focus while the aperture changes.

 

LJ

 

P.S. The back/frontfocus issue is separate from the focus shift when stoppng down, which fast lenses are more susceptible to in general. However, Leica glass seems to have a much larger shift in focus than others I have used. Also, the backfocus issue also seems to be much more pronounced on more Leica lenses....at least as folks are reporting. Something does not seem "right" about all of this, and Leica, in my mind, should be looking into all of this with a bit more care than seems to be expressed by others. One should not have to send in a lens several times to fix things that were not previously broken, nor should one have to send in the camera body to be calibrated with specific lenses. If things are that far off, then the range of tolerances may be too large, or more possibly, the lenses are not leaving the factory properly calibrated from the start.

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The two terms "focus shift" and "back focus" are used interchangeably but to my mind they are actually two distinct phenomena which will spoil your day.

 

With Focus Shift, the plane in focus moves as you stop down the lens. It's a characteristic of the lens formulation and the hope of the designer is that the increasing depth of field as you stop down will mask the effect. Unfortunately, the reduced depth of focus with digital is making it more noticeable than it would otherwise be.

 

Back Focus is down to an alignment problem in the camera or with your eye-sight. You have turned the focus ring on the lens so you are as certain as you can be that the rangefinder patch aligns with the main image in the viewfinder but unfortunately, due to a misalignment of the lens or the camera or your eye-sight, the image projected by the lens onto the sensor is not in focus.

 

In this respect, a rangefinder is at a disadvantage compared to a dSLR because with a rangefinder, you are using a proxy for focus indication, not the actual image rendered by the lens.

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Mark,

You are absolutely correct on both items here, and I know I intertwined them in my discussion a bit. The Focus Shift is lens design related, yet it seems far more prevalent in Leica lenses than in some others. The lessend DOF from the digital sensor argument does have impact here, yet the overall design of some lenses still suggests others are not having as much of a problem as Leica is.

 

The Back Focus issue also seems to be more problematical with Leica lenses, as reported by others here, and from my very limited test group myself. All of the things you mention (alignment, rangefinder calibration and eye-sight) should also come into play with any lens used on the camera body, no? So if one is not having those sorts of problems with othere lenses, that starts to narrow the issue more to the lens being more the problem. I do not have any issues with any other lenses except my 75 Cron. That suggests to me that the focus on the Cron is not properly set or calibrated.

 

This is what I think more than a few folks here are experiencing. Some Leica lenses they have, be it the 35/1.4, 50/1.4, 75/1.4 or whatever, have pronounced back focus issues beyond the Focus Shift issues. When you get both happening, it is doubly frustrating.

 

I agree with you that we should be more careful in our discussions about which issue, and I am guilty as charged for mixing them together in my discussion. However, that does not absolve the other problems, which seem to be Leica related.....spotty QC and possibly poor calibration of some lenses to start.

 

Again, thank you for helping keep the issues properly separated.

 

LJ

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The two terms "focus shift" and "back focus" are used interchangeably but to my mind they are actually two distinct phenomena which will spoil your day.

 

 

Right they are totally two different things. Everyone is noticing the focus shift when stopping down on the M8 because of the instant feedback where with film, shooting 24 or 36 exposure rolls, there was X amount of time betwen the shutter push and when you actually got to view the shot. So with the longer time between the 2 you would forget and say, "I guess I really didn't nail the focus opn that one", and because film has depth it wasn't as noticeable.

 

Backfocus again wasn't as noticeable because of the depth of the film along with the time involved from shot taken to develope time.

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Ed,

The backfocus problem on your 75 cron was similar to the problem I had when I bought a used 75 lux. Minimum backfocus close in but feet apart after a distance. I used the M8 rangefinder tweak to correct. Now it's spot on.

 

With backfocus, even if the factory starts calibrating the new M8s and new lenses to a closer tolerance, there are thousands of used lens stock out there that have to be matched to the bodies and to each other.

 

Jan

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I haven't had a focusing issue on my M8 with any of the Leica lenses I have owned, including the 75 lux, 35 lux asph, 28 cron, 50 rigid summicron, 90 elmar macro or 35 summicron IV.

But I did recently return a CV 40 because it was focusing an inch or two behind the spot I was aiming for at f/1.4.

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Ed,

The backfocus problem on your 75 cron was similar to the problem I had when I bought a used 75 lux. Minimum backfocus close in but feet apart after a distance. I used the M8 rangefinder tweak to correct. Now it's spot on.

 

 

Jan

 

Well I'm not going to start tweaking the wheel because it is only the 75mm that shows this back focus all other lenses are fine. 90 TE 2.8, 50 cron and 35 cron ASPH focus spot on at all distances I've check them on (haven't bothered checking the 28/2.8 ASPH or the 24/2.8 ASPH because the DOF on those lenses make up for any BF they may have and I have not had any shots from those 2 WIDE lenses that I would call OOF).

And since I have 2 M8's and the 75 does the exact same thing on both bodies it's not a rangefinder adjustment.

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Right they are totally two different things. Everyone is noticing the focus shift when stopping down on the M8 because of the instant feedback where with film, shooting 24 or 36 exposure rolls, there was X amount of time betwen the shutter push and when you actually got to view the shot. So with the longer time between the 2 you would forget and say, "I guess I really didn't nail the focus opn that one", and because film has depth it wasn't as noticeable.

 

Backfocus again wasn't as noticeable because of the depth of the film along with the time involved from shot taken to develope time.

 

Ed,

While I understand your agrument, I am not sure I completely agree here. If I were shooting film today on a camera that was set up just like the M8, I am sure I would be very unhappy the next day or several days later to see as many Back Focus problems, as I am not sure the thickness of the film ever overcomes that problem. If the plane of focus is that far off, the film is not going to correct that. The Focus Shift issue would still be a problem, but as you suggest, it might be a bit less noticeable. When I used to shoot Leicas for my PJ work long ago, I do not recall ever thinking about either of these problems, and for sure, not the backfocus issue. If all my shots were off, I would have been screaming to get things fixed. As it was, I almost never had that sort of problem, yet I do have it today on the M8, but only with a Leica lens.

 

As I think about this more and more, I start to wonder why this is a bigger problem than before. Your argument about our maybe not noticing or remembering things days or more later when the film came back can account for some things that we may have chaked up to focus error on our part, and yes, the instant feedback on the LCD makes it more pronounced. However, anybody shooting with any regularity, and shooting a lot of film would have been seeing some of the problems. So, the problems may have always been there, but are more readily seen and reported today, with the M8, due to the instant feedbak and our ability to do a lot more pixle peeping on monitors at larger magnifications. That still does not explain why there does not seem to be as much of an issue with many non-Leica lenses.

 

LJ

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I agree with you. I really think that Leica has gone down hill from the old days. Remeber that Leica was almost out of business a couple of times in the last 10 years and if the M8 had not come out and been adopted by so many of use they may not have been in business today.

 

Stephen Lee has to do something about QC. It's hard to beleave that one person can get a series of lenses, the same lens FL and aperture, and have them all show a big focus shift when someone else gets the same type lens and it show very little FS.

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I too am surprised that we don't hear of people sending their Zeiss and CV lenses back for adjustment. Aside from quality control issues at Leica, I think it's down to the speed of the lenses. The ones we worry about most are f1, f1.4, f2 whereas the majority (but not all) of Zeiss and CV lenses are f2 or smaller. A smaller aperture lens will display less focus shift and the focussing adjustment is less critical, making things altogether easier to deal with.

 

That's why (and I know HC doesn't agree with me) I think lenses like the 35/1.4 need to be redesigned for digital to take account of these issues which are assuming greater significance in the era of the M8.

 

In the future, Leica should replace the expensive mechanical rangefinder with an electronic one; the camera could then be taught - fine tuned - to each individual lens you put on it. If you were able to dial in +/- back focus adjustment at a set of pre-defined target distances, the camera could learn how, for this lens, the focussing characteristic deviates from normal.

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The two terms "focus shift" and "back focus" are used interchangeably but to my mind they are actually two distinct phenomena which will spoil your day.

 

It is important not to confuse the two. Moreover, anyone working with a camera that has an out of adjustment RF may have some trouble knowing which problem is affecting their pictures. A camera with a mis-adjusted RF can actually have a lens come into better focus as it shifts focus with decreasing aperture.

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Ed,

So, the problems may have always been there, but are more readily seen and reported today, with the M8, due to the instant feedbak and our ability to do a lot more pixle peeping on monitors at larger magnifications.

 

LJ

 

That's important to keep in mind. Looking at digital files at 100% places more demands upon them than most contact prints or enlargement prints do. The M8's very strong resolution and lack of AA filter is also relentless in revealing these differences.

 

Cheers,

 

Sean

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It is the unfortunate truth that Leica has not got it's product portfolio sorted for the M8.There are too many lenses that do not focus accurately with the M8, and to be honest I don't care if it is the rangefinder or the lens..the combination does of M8 and existing and used lenses is simply inconsistent.Half of my lenses do not focus accurately.

On top of that I arrived yesterday in Tel Aviv for a weeks trip and my M8 failed me again today, for the 2nd and last time.I personally have given up with this system as much of the advantages I had hoped for are not there.

I am shooting today and for the rest of the week with a simple laughable Canon 350d and 35mm lens.It works and for all its enemies, it just is the lightweight, low noise reliable camera.(I let the 5d at home because ot was too big,,LOL.)

You'll see my M8 on ebay soon as it comes back from it's 2nd trip from Solms...enough is enough.

For me it is clear the Leica has bitten off more than they can chew.

M6 and 5D/350D is the way to go for me..your view may of course differ.

 

Am I having a rant , yes...is it justified, yes.

 

good luck with your backfocus and beware of people who tell you you need a 1.25 finder for accurate focus or you need to 'squeeze' the shutter to get sharp images.

 

Best Regards

Andy

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I too am surprised that we don't hear of people sending their Zeiss and CV lenses back for adjustment. Aside from quality control issues at Leica, I think it's down to the speed of the lenses. The ones we worry about most are f1, f1.4, f2 whereas the majority (but not all) of Zeiss and CV lenses are f2 or smaller. A smaller aperture lens will display less focus shift and the focussing adjustment is less critical, making things altogether easier to deal with.

 

Actually, the CV 35/1.2 focuses spot on with virtually no focus shift as it is stopped down. Ditto for the 28/1.9, 35/1.7 and 50/1.5. See the 35 mm review but max aperture is probably a red herring here. Various people who have sometimes referred to CV lenses as being "off brand" and "second rate" must be scratching their heads on this one a bit.

 

There's some minor shift in the Zeiss 35/2.0 and CV 40/1.4.

 

The reality, which I hope gradually gains wider acceptance, is that various lenses have strengths and weaknesses and this is not always correlated with who makes them or what they cost. Status, cost and performance aren't always matched.

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On top of that I arrived yesterday in Tel Aviv for a weeks trip and my M8 failed me again today, for the 2nd and last time.

 

OT, I know, but what happened to it? I've been curious to know if the failures I wrote about earlier this year are still happening. Knock wood, but the current example I have is fine. What's your firmware BTW? We can move this to another thread if you like.

 

Cheers,

 

Sean

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Sean

SW V1.102

The same thing happened as last time.

 

Switch on the camera, prepare to take a shot, the display shows the menu (?)and press the shutter, nothing happens, meaning display continues to show menu and shutter does not releaase.Yes, the battery was charged.

 

Turn camera off and menu menu display is still showing.(the camera is swithched off !)Take battery out , wait and replace, same thing.Try again same thing.

Take out 350d , switch on and take photographs.

Tomorrow off to Jerusalem, will probably buy a cheap WA not to miss too many opportunities...

 

regards

andy

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