24-90mm Focus Shift (Diglloyd)

[G. van Asch]

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I think the first one is AF. Because I also tested for me there is hardly any difference.

Gerjan

[LocalHero1953]

Hi namesake - are you only seeing this at distance or at close up as well?

(####369.jpg is clearly softer.)

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[tashley]

I think the first one is AF. Because I also tested for me there is hardly any difference.

Gerjan

 

I'm not of the opinion that in my two examples there's 'hardly any difference'.... for me the difference is between a $400 kit lens and something costing quite a lot more....

[LocalHero1953]

Hi namesake - are you only seeing this at distance or at close up as well?

(####369.jpg is clearly softer.)

Rereading what I posted: soft is the wrong word - it is fuzzy - unacceptably so, I agree.

[cpclee]

I did a quick (and sloppy) sloping target test as suggested by thighslapper.  The target was sloped at roughly 45 degrees and I focused on the "o" in the word "over".  This was at 90mm and f4.0.  Target was probably just 1.5-2ft  away.

 

 

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[cpclee]

I took 5 shots each time refocusing by AF.  In each picture the "o" looks to me like the point of best focus, as in this picture.  So in short I wasn't able to replicate the issue being discussed.

 

But it did occur to me that while the selected (central) crosshair more or less covered the "o" exactly, the little box enclosing that crosshair covered as far down as half of the "W' and as far up as half of the "7" and similarly sideways.  My thinking is the CDF algorithm tries to maximize contrast within that box and not just what's covered by the crosshair.  One might be quick to assume that since the crosshair is at the center of the box, the point of best focus should fall exactly there when the CDF maximizes the contrast within the whole box.  But mathematically that is not true.  When total contrast within that box is maximized, some point in that box will be the point of best focus, but that some point doesn't have to be at the center of the box.  It all depends on how contrast is distributed within that box in the current scene.

 

I am not an engineer specializing in this, but mathematically I'm inclined to think that is how contrast detection works.

 

So for those of you who found your AF to front focus, you want to check whether the point of best focus, despite not where you thought it should be, isn't still inside the little box enclosing your selected crosshair.  If it is in inside the box, then this is not a bug but more of a confusing design choice.  

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Edited March 5, 2016 by cpclee

[tashley]

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Cpclee, that may or may not be the case but these things manifest differently at different distances and with planar subjects that are parallel to rather than sloping away from the sensor. The correct way to check for poor focus, focus shift or front/back focus is to use a planar target with a ruler attached on a slope at the side, with the planar part exactly placed over a zero mark on the ruler. I have such a device but haven't bothered to run that test because imho if the camera's AF system can't hit a brick s*** house at twenty paces then it's not much use to me, however well it might do at close up non-planar targets. But we all expect different things from our gear!

[ramarren]

Curious about the comments from people who aren't seeing this problem at longer distances in the real world, I banged off a quick comparison this morning. Distance to subject is very close to 235 metres. Guess which one is manual and which auto-focus? It was this sort of thing that I experienced on walkabout shooting that encouraged me to start reading up and then testing.

 

http://tashley1.zenfolio.com/img/s4/v9/p1782968203.jpg

 

http://tashley1.zenfolio.com/img/s3/v42/p1646823769.jpg

 

 

I certainly see the difference in those images, Tim. I just don't see similar differences in my images. 

 

Part of this is my expectations, I'm sure. When I use AF, I let it lock in then adjust the fine focus until my eye is satisfied. I never expect AF to get it perfect... and am pleasantly surprised when it does. To me, AF is a nice aid to be used when appropriate, not an essential to getting sharp images. 

 

Since the lens, focused manually, can achieve perfect critical focus at all distances, it's obvious to me that these issues are matters of AF system tuning. I'm certain that Leica has received enough input on this topic that they are working on it and that it will shortly be resolved. 

[tashley]

Ramarren, if I ever start a camera company I will be sure to invite you to the launch and then to assiduously court your custom!

Edited March 5, 2016 by tashley

[jrp]

I know it doesn't help, but my 90mm shots are above my expectations. I would have been as disappointed as you are if my results were like the test shots you show. 

[cpclee]

I had reported earlier that with a planar target I saw no systematic discernible difference between AF and MF results.

 

Again I think the difficulty that people are experiencing may be explained by how Leica uses crosshairs to represent AF points.  Look at the first picture.  The CDF area is actually that whole box enclosing the selected crosshair, and as such so long as the point of best focus falls inside that box everything is fair games.  If that box happens to contain things with varying distances to the camera then you need to be careful. (For example, if the crosshair aiming at the guy's chin is selected. That box contains not just the chin but also some of the background.) But by using crosshairs as representation, the photographer is invited to think that the point of best focus will fall exactly where the crosshair is which is very misleading.  The crosshair is only a small part of the box.

 

The second picture shows you the AF system of the Sony A7 family which uses both CDF and phase detection simultaneously.  The CDF points work the same way and are roughly the same size as the SL's but are represented more intuitively as boxes.  With this design, the photographer would have no reason to assume the point of best focus has to be at the center of the selected box.  In fact, look at how much finer the phase detection points are.  That is to address precisely the issue I just described. The CDF focus points by nature cover a relatively wide area.  When a CDF box is selected, the point of best focus may still fall inside any of the small phase-detection boxes and therefore not in the center of the CDF box.

 

This points to a UI design flaw rather than a failure of the AF system per se.  

 

 

Cpclee, that may or may not be the case but these things manifest differently at different distances and with planar subjects that are parallel to rather than sloping away from the sensor. The correct way to check for poor focus, focus shift or front/back focus is to use a planar target with a ruler attached on a slope at the side, with the planar part exactly placed over a zero mark on the ruler. I have such a device but haven't bothered to run that test because imho if the camera's AF system can't hit a brick s*** house at twenty paces then it's not much use to me, however well it might do at close up non-planar targets. But we all expect different things from our gear!

 

 

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[k-hawinkler]

 

 

Curious about the comments from people who aren't seeing this problem at longer distances in the real world, I banged off a quick comparison this morning. Distance to subject is very close to 235 metres. Guess which one is manual and which auto-focus? It was this sort of thing that I experienced on walkabout shooting that encouraged me to start reading up and then testing.

 

http://tashley1.zenfolio.com/img/s4/v9/p1782968203.jpg

 

http://tashley1.zenfolio.com/img/s3/v42/p1646823769.jpg

 

Hi Tim.  

To me p1782968203.jpg looks focused correctly, whereas p1782968203.jpg isn't.

I would consider the latter image of unacceptable quality.  

My Sony A7r2 certainly does way better than that.

It seems to me they sold you a lemon.

Sorry about that.

[ramarren]

Ramarren, if I ever start a camera company I will be sure to invite you to the launch and then to assiduously court your custom!

 

 

If more companies did that, the cameras would work better for me and I'd have bought fewer of them. 

Oh, uh, wait ... That's probably not what they want! 

[ramarren]

I had reported earlier that with a planar target I saw no systematic discernible difference between AF and MF results.

 

Again I think the difficulty that people are experiencing may be explained by how Leica uses crosshairs to represent AF points.  Look at the first picture.  The CDF area is actually that whole box enclosing the selected crosshair, and as such so long as the point of best focus falls inside that box everything is fair games.  If that box happens to contain things with varying distances to the camera then you need to be careful. (For example, if the crosshair aiming at the guy's chin is selected. That box contains not just the chin but also some of the background.) But by using crosshairs as representation, the photographer is invited to think that the point of best focus will fall exactly where the crosshair is which is very misleading.  The crosshair is only a small part of the box.

 

The second picture shows you the AF system of the Sony A7 family which uses both CDF and phase detection simultaneously.  The CDF points work the same way and are roughly the same size as the SL's but are represented more intuitively as boxes.  With this design, the photographer would have no reason to assume the point of best focus has to be at the center of the selected box.  In fact, look at how much finer the phase detection points are.  That is to address precisely the issue I just described. The CDF focus points by nature cover a relatively wide area.  When a CDF box is selected, the point of best focus may still fall inside any of the small phase-detection boxes and therefore not in the center of the CDF box.

 

This points to a UI design flaw rather than a failure of the AF system per se.  

 

 

AF is simply imprecise unless you have a true "point AF" capability you can use. It's a lack of understanding and overly optimistic expectations that does us wrong, IMO. 

 

I have used many AF cameras, some very highly touted. I've seen the AF fail to give the best results with all of them a good bit of the time, even though the lens and camera were otherwise excellent performers. 

[tashley]

Cpclee and ramarren,

 

I think (hope?) that most of us here probably understand that the AF 'points' (whether represented by a crosshair or a small box) on modern cameras (whether using PDAF or CDAF or hybrid) are actually not points at all, but small areas. I also think that it's mostly understood that as soon as the photographer is working with an area and not a point, the chance arises that parts of the subject field which stand at differing distances from the sensor might both/all fall within that area and therefore provide room for ambiguity and therefore apparent error. For those of us who generally use AF rather than AF with MF tweak or pure MF, we need to be alive to this possibility and to use the AF system accordingly. This is why both of my examples have used planar targets and why, when testing for, for example, focus shift, we need to work with equipment such as a Spyder Lenscal. Even then we need to be aware of the possibility of field curvature in the optic, and of the fact that field curvature can be very complex and can change at differing distances and apertures.

 

It is, however, my experience with my other current equipment (Sony A7RII and Nikon D810) that modern systems have a very very high rate of accurate AF provided that the photographer understands their strengths and limitations and uses them accordingly.

 

It is also my firm opinion that, the SL is not particularly well suited to 'AF and then MF refinement before shot' because it has no split screen or prism and no ability to trigger magnification with a twist of the MF ring other than by button presses (I assumed it would have this but haven't yet found it. If I'm wrong, I stand corrected and would like to know how to achieve it.)

 

In other words, the marketing materials of the camera and the operational design of the camera (not to mention its price) taken into conjunction with the performance of its peer group ( which I'd mainly consider to be any high DSLR or mirrorless, most specifically the D5/1DX type camera but also D800 and Sony A7 series) strongly lead one to expect that it will have accurate AF when deployed correctly and under appropriate conditions. 

 

According to my pretty appropriate testing, my copy does not. One hears from some other people that theirs do not, either, including some fairly well-qualified testers. One also hears that Leica is aware of a focus bug and is working on correcting it. It seems therefore to me most likely to be the case that there is a bug and that if that bug is software based, it is universal and that, therefore, those who do not experience it are either lucky, shooting subject matter that doesn't trigger it, or simply not noticing it.

 

Nonetheless I will proceed with the hypothesis that there is a bug and that it does mean that, at least at the long end, a certain and significant proportion of images made within the normal shooting envelope of the camera will not be as well focussed as the lens is capable of and the punter has a reasonable right to expect.

 

If that hypothesis is correct, the question for each of us becomes 'should I put up with it until it is fixed?'

 

My personal answer to that is, 'no'. My reasons are that it doesn't work properly and that I need it to and that at the price I paid, I have a right to expect it to - as is indeed the fact, I believe, in consumer law. Hence my intention to return mine rather than wait for the outcome of an extensive beta program for new firmware, during which time my 'return window' might well close and during which time I will have a system that doesn't work properly.

 

Rammaren feels differently - seemingly unbothered by the problem, happy to use the camera differently and to await a fix. I get that. I drive a Tesla and it has satnav which is often so bad that it makes you laugh. I know of Tesla drivers who love their vehicles so much that they install TomTom systems or similar in order to make up for the failings of the built-in system. These things are highly personal and each of us is more or less in thrall to the gestalt of the brands to which we subscribe.

 

But I think it's important to separate these threads out. Can modern AF systems be misunderstood and therefore give unexpectedly poor results when used incorrectly? Yes. Can you test to ex-out that as a factor thereby determining not whether the system was correctly used but whether it correctly functions? Yes. Does the SL pass that latter test? For at least some of us, no. Does that matter? Yes or no, depending on what each of us expects for her/his money and how each of us uses the camera. But let's not muddy the waters by a mixed bag of implications that the 'problem' either doesn't exist or doesn't matter. Please.

Edited March 6, 2016 by tashley

[ramarren]

Cpclee and ramarren,

 

I think (hope?) that most of us here probably understand that the AF 'points' (whether represented by a crosshair or a small box) on modern cameras (whether using PDAF or CDAF or hybrid) are actually not points at all, but small areas. I also think that it's mostly understood that as soon as the photographer is working with an area and not a point, the chance arises that parts of the subject field which stand at differing distances from the sensor might both/all fall within that area and therefore provide room for ambiguity and therefore apparent error. For those of us who generally use AF rather than AF with MF tweak or pure MF, we need to be alive to this possibility and to use the AF system accordingly. This is why both of my examples have used planar targets and why, when testing for, for example, focus shift, we need to work with equipment such as a Spyder Lenscal. Even then we need to be aware of the possibility of field curvature in the optic, and of the fact that field curvature can be very complex and can change at differing distances and apertures.

 

It is, however, my experience with my other current equipment (Sony A7RII and Nikon D810) that modern systems have a very very high rate of accurate AF provided that the photographer understands their strengths and limitations and uses them accordingly.

 

It is also my firm opinion that, the SL is not particularly well suited to 'AF and then MF refinement before shot' because it has no split screen or prism and no ability to trigger magnification with a twist of the MF ring other than by button presses (I assumed it would have this but haven't yet found it. If I'm wrong, I stand corrected and would like to know how to achieve it.)

 

In other words, the marketing materials of the camera and the operational design of the camera (not to mention its price) taken into conjunction with the performance of its peer group ( which I'd mainly consider to be any high DSLR or mirrorless, most specifically the D5/1DX type camera but also D800 and Sony A7 series) strongly lead one to expect that it will have accurate AF when deployed correctly and under appropriate conditions. 

 

According to my pretty appropriate testing, my copy does not. One hears from some other people that theirs do not, either, including some fairly well-qualified testers. One also hears that Leica is aware of a focus bug and is working on correcting it. It seems therefore to me most likely to be the case that there is a bug and that if that bug is software based, it is universal and that, therefore, those who do not experience it are either lucky, shooting subject matter that doesn't trigger it, or simply not noticing it.

 

Nonetheless I will proceed with the hypothesis that there is a bug and that it does mean that, at least at the long end, a certain and significant proportion of images made within the normal shooting envelope of the camera will not be as well focussed as the lens is capable of and the punter has a reasonable right to expect.

 

If that hypothesis is correct, the question for each of us becomes 'should I put up with it until it is fixed?'

 

My personal answer to that is, 'no'. My reasons are that it doesn't work properly and that I need it to and that at the price I paid, I have a right to expect it to - as is indeed the fact, I believe, in consumer law. Hence my intention to return mine rather than wait for the outcome of an extensive beta program for new firmware, during which time my 'return window' might well close and during which time I will have a system that doesn't work properly.

 

Rammaren feels differently - seemingly unbothered by the problem, happy to use the camera differently and to await a fix. I get that. I drive a Tesla and it has satnav which is often so bad that it makes you laugh. I know of Tesla drivers who love their vehicles so much that they install TomTom systems or similar in order to make up for the failings of the built-in system. These things are highly personal and each of us is more or less in thrall to the gestalt of the brands to which we subscribe.

 

But I think it's important to separate these threads out. Can modern AF systems be misunderstood and therefore give unexpectedly poor results when used incorrectly? Yes. Can you test to ex-out that as a factor thereby determining not whether the system was correctly used but whether it correctly functions? Yes. Does the SL pass that latter test? For at least some of us, no. Does that matter? Yes or no, depending on what each of us expects for her/his money and how each of us uses the camera. But let's not muddy the waters by a mixed bag of implications that the 'problem' either doesn't exist or doesn't matter. Please.

 

 

That's a lot of words to say, "Hey, I am upset enough by the AF on this camera that I don't want the camera." 

 

In my use of the SL with the 24-90mm lens, the AF has performed very well and very accurately. I don't need any focusing aids to manually focus a 90mm lens with the SL's viewfinder either, so if the AF's lock-in setting requires a tweak, I find it easy to tweak to critical focus. Thus, in normal use, the camera and lens perform as I expect and I'm satisfied with it. 

 

If the camera doesn't work to your expectations, sell it. Easy.

[tashley]

Yup, I think we'd already established that your expectations are lower than mine! But if you can't see the contradiction between

 

"In my use of the SL with the 24-90mm lens, the AF has performed very well and very accurately." 

 

and

 

"if the AF's lock-in setting requires a tweak, I find it easy to tweak to critical focus"   then I can't help you!

Edited March 6, 2016 by tashley

[ramarren]

Yup, I think we'd already established that your expectations are lower than mine! But if you can't see the contradiction between

 

"In my use of the SL with the 24-90mm lens, the AF has performed very well and very accurately." 

 

and

 

"if the AF's lock-in setting requires a tweak, I find it easy to tweak to critical focus"   then I can't help you!

 

 

Is it necessary to become insulting and move to puffery, Tim?

 

As I have said before, I've found that all AF systems make errors. In those cases you need to tweak the focus to get the results you want. If you're expecting perfection, you should likely not bother with camera equipment. 

[tashley]

Is it necessary to become insulting and move to puffery, Tim?

 

As I have said before, I've found that all AF systems make errors. In those cases you need to tweak the focus to get the results you want. If you're expecting perfection, you should likely not bother with camera equipment. 

 

Dear me, no insult intended, merely drawing your attention to the contradictions in what you have said. It can't be rude to state the facts, surely?

 

And as I have said, my points of reference are peer group cameras that generally, usually, in fact pretty much always manage to AF accurately when used within their design envelope whereas my SL and @ 90mm lens' default mode is not to do so. That is why it is, as I understand the current state of play, acknowledged as a known fault which is under investigation for a solution. My expectations appear, therefore, to be in line with Leica's expectations of their own product. The fact that they are higher than yours is a matter of personal choice on both our parts!

Edited March 6, 2016 by tashley

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[CheshireCat]

Leaving to one side the accuracy of the placing of the focus point, focus shift seems to be a feature of almost every lens, particularly non-APO lenses.

 

 

A lot of confusion in this thread.

 

The term "focus shift" is unfortunately used to describe different problems:

- Different focus plane for different spectrum frequencies (mitigated with APO lenses).

- Different focus plane for all spectrum frequencies at different lens apertures (mitigated with asphericals).

 

In this thread, I understand we are discussing the second one. And the second one is defenitely not a feature of every lens, especially those that don't feature an ultra-wide-aperture like the lens in question.

 

And it does not help at all to use the term "focus shift" also to describe the other SL firmware issue that displays the focus point indicator in the wrong place when magnification is active. That issue should be called "wrong focus point display position".