Focus Fine Tune

Started 5 months ago | Discussions
richiebee
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Focus Fine Tune
5 months ago

So this is a relatively recent addition at least to consumer level cameras, presumably because the resolution has become significant enough to show problems in lens focus.

For those who have the function, I'm curious as to whether you use it, or leave it alone.

R.

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darklamp
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Should be avoided by inexperienced users
In reply to richiebee, 5 months ago

So this is a relatively recent addition at least to consumer level cameras, presumably because the resolution has become significant enough to show problems in lens focus.

No, that's not what it's for.

It's because the tolerances to which lens mounts and lenses are made make it impossible to guarantee that the intended focal plane will be precisely where the designers intended.

For the vast majority of camera and lens combinations the differences are not detectable outside a lab, and certainly are less than the normal errors due to user error ( wrong focus point, depth of field issues, etc. ).

But for those unfortunate combinations where the tolerances combine to make the effect worse, the facility to adjust focus in this way exists.

For those who have the function, I'm curious as to whether you use it, or leave it alone.

It should be noted that detecting and correctly diagnosing the issue is something that the vast majority of inexperienced users will get completely wrong. Inexperienced users should not use micro focus adjustment.

Beginners like to blame the equipment. The reality is that focus issues are almost all caused by the user's lack of skill, wild expectations and lack of key knowledge ( like depth of field ) which they never bother to learn.

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richiebee
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Re: Should be avoided by inexperienced users
In reply to darklamp, 5 months ago

Why is it only a recent addition?

And to answer the question.  Do you have it, do you use it?

darklamp wrote:

So this is a relatively recent addition at least to consumer level cameras, presumably because the resolution has become significant enough to show problems in lens focus.

No, that's not what it's for.

It's because the tolerances to which lens mounts and lenses are made make it impossible to guarantee that the intended focal plane will be precisely where the designers intended.

For the vast majority of camera and lens combinations the differences are not detectable outside a lab, and certainly are less than the normal errors due to user error ( wrong focus point, depth of field issues, etc. ).

But for those unfortunate combinations where the tolerances combine to make the effect worse, the facility to adjust focus in this way exists.

For those who have the function, I'm curious as to whether you use it, or leave it alone.

It should be noted that detecting and correctly diagnosing the issue is something that the vast majority of inexperienced users will get completely wrong. Inexperienced users should not use micro focus adjustment.

Beginners like to blame the equipment. The reality is that focus issues are almost all caused by the user's lack of skill, wild expectations and lack of key knowledge ( like depth of field ) which they never bother to learn.

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darklamp
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Re: Should be avoided by inexperienced users
In reply to richiebee, 5 months ago

Why is it only a recent addition?

It's not exactly a new feature as you could access this through debug menus ( if you knew how to do that ) on many models for a long time now.

Like many features it has been creeping down from top end gear to low end gear as the marketing departments try to add things to draw customers. However it is notable that more useful photographic features are used as a primary differentiator between different pricing tiers. This should tell you how relatively minor a feature MFA is.

Note that MFA is generally regarded as pretty pointless with a zoom lens, as you can only set a correction for a given focal length in the range. In doing so you're likely to change the behavior at all focal lengths in the range.

So it's really a very specialized tool.

And to answer the question. Do you have it, do you use it?

What difference does it make to you if I ( or anyone else ) uses something ?

Either you need it or you want it or you don't.

Most beginners should, as I have said, avoid this feature like the plague. Not having would not cripple their photography, IMO. In fact it's a distraction from identifying the real ways to improve their photography.

It's like people trying to improve their cornering by fine tuning the suspension instead of looking at how they handle the steering wheel. The former only works if you've already nailed the later.

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richiebee
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Re: Should be avoided by inexperienced users
In reply to darklamp, 5 months ago

Actually, I don't care whether you use it or not.  Sorry I had the audacity to ask such a personal question.

darklamp wrote:

What difference does it make to you if I ( or anyone else ) uses something ?

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ajscullard
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Re: Focus Fine Tune
In reply to richiebee, 5 months ago

I'm with darklamp on this one. Microfocus Adjustment is primarily there to help experienced users or professional technicians to compensate for tolerance mismatches between bodies and lenses.

OK, I've got many years of camera experience from manual focus lenses on 35mm and 6x6 medium-format film cameras through to top-end full-frame digital autofocus, so if I get a shot that isn't sharp I can figure out what the problem was. And I've never known it to be the fault of the camera or the lens.

So for a long time I didn't attempt any micro-adjustment as I figured I could only make things worse. But Reikan's FoCal software gave me a recoverable way to try it out. It worked fine on one camera body (Canon 1DsIII) and a set of "L" lenses but failed totally with the same lenses on another version of exactly the same camera body (go figure). Reikan support wasn't able to find the reason or a cure, but I may try it again sometime.

Did the MA make any discernible difference? Well, the numbers showed that most lenses were adjusted by a small amount, and one or two lenses had a fairly large (>10) adjustment. However in practice I didn't see a major difference. If the shots weren't in focus it was still down to my error, one way or another (too low a shutter speed, bad placement of focus point, etc.). In some critical situations (narrow DOF) there was a small improvement. Probably worth the investment in money and time, so no complaint about the software.

As darklamp says, unless you really know what you are doing and you have sufficient experience to analyse your results well enough to ascertain correctly why a shot is not sharp enough, then you need to think carefully about dong any MA. You may end up making things worse so be sure you have some way of resetting the lens(es) to the original settings.

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EinsteinsGhost
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In reply to richiebee, 5 months ago

So this is a relatively recent addition at least to consumer level cameras, presumably because the resolution has become significant enough to show problems in lens focus.

For those who have the function, I'm curious as to whether you use it, or leave it alone.

R.

If you have a lens that is back/front focusing, this is the tool to use to correct it. I have found the issue to be rare but even one occurence can be frustrating as I found when using a 25+ year old Minolta 24-50/4 on my Sony NEX-6 (via LAEA2 adapter, which is a smart adapter to use Minolta/Sony A-mount lenses on Sony E-mount cameras with fast mirror based PDAF). The adapter has AF Microadjust feature. With a little corrective effort, the lens now is as accurate in focusing where I point it, as it should be. So, use it, if your camera (and in my case, the adapter) has it.

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GodSpeaks
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Re: Focus Fine Tune
In reply to richiebee, 5 months ago

richiebee wrote:

For those who have the function, I'm curious as to whether you use it, or leave it alone.

Yes, I use it. Very easy to do, just read up before hand so you know what you are doing.

Personally I use the FoCal software which pretty much automates the process and takes the guess work (human error) out of the process.

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Chris R-UK
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Re: Should be avoided by inexperienced users
In reply to richiebee, 5 months ago

I agree with darklamp on this subject.

There have been many threads on these forums from beginners who have meddled with MFA when their actual focus problems were caused by technique, not body/lens miscalibration.  I have tried recalibrating one of my lenses using MFA and my experience has been the same as others on this thread - I couldn't see any difference after the MFA calibration.

MFA is relatively new and professional photographers have been able to produce great shots from SLRs for many, many years without the benefit of MFA.

Note that MFA only applies to PDAF systems as used on DSLRs.  CDAF systems as used on all mirrorless cameras (including compacts) are not affected by any body/lens miscalibration.

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richiebee
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Re: Focus Fine Tune
In reply to ajscullard, 5 months ago

Interesting.  The implication here and the suggestion in others posts is that this is somehow semi-destructive.  On my camera, all lenses start with a value of zero, and you can offset each lens (which gets recognized by the camera when its attached) using a single parameter slider.  Resetting the value to zero for each lens (or I suspect resetting the camera itself will put all lenses back to default) is all that is needed to return it to its original position so I don't get the need to be so careful here.  You're not taking a screwdriver to anything.  

Is it done differently on other cameras?

R.

ajscullard wrote:

As darklamp says, unless you really know what you are doing and you have sufficient experience to analyse your results well enough to ascertain correctly why a shot is not sharp enough, then you need to think carefully about dong any MA. You may end up making things worse so be sure you have some way of resetting the lens(es) to the original settings.

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MediaArchivist
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In reply to darklamp, 5 months ago

I have it, and I have used it. I used it incorrectly, and then correctly

When I got my first wide aperture lens (f/1.4) I noticed a lot of missed focus shots. I had never used f/1.4 before, being unaccustomed to narrow DoF I simply assumed it was the lens (or camera). I fiddled forever with the micro-adjust and it did not help at all.

Later, I got more used to the narrow DoF and started to get a lot more keepers. Still, for some lenses (more older lenses from the 1980's and 1990's) the AF was a little off. So I revisited micro adjust again, but was much more rigorous. I got a focus test board, the kind with an angled and marked section, and ran carefully controlled tests at various distances. I repeated the tests several times. A few of my lenses have a micro-adjust in place, most of them don't.

If you are going to mess with it, do it right. Confirm that you have a problem and can assign a number to the problem. Some lenses will act differently from MFD than from infinity. Some are a little off, plus or minus, every time— so micro adjust won't help. For those lenses I use focus peaking and if my subject is not peaked when I get focus lock, I refocus.

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EinsteinsGhost
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Re: Should be avoided by inexperienced users
In reply to Chris R-UK, 5 months ago

I agree with darklamp on this subject.

There have been many threads on these forums from beginners who have meddled with MFA when their actual focus problems were caused by technique, not body/lens miscalibration.  I have tried recalibrating one of my lenses using MFA and my experience has been the same as others on this thread - I couldn't see any difference after the MFA calibration.

MFA is relatively new and professional photographers have been able to produce great shots from SLRs for many, many years without the benefit of MFA.

Note that MFA only applies to PDAF systems as used on DSLRs.  CDAF systems as used on all mirrorless cameras (including compacts) are not affected by any body/lens miscalibration.

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Chris R

That contradicts the fundamental premise of "opposition". If pros don't need it, then the cameras they use should be the last place for including MFA. Yet, they all have access to it, and are better served using that feature.

Someone new to the concept, should also learn and take advantage of the feature if they have the need to do so. Continuing to shoot with a backfocusing set up only to blame self makes zero sense.

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mosswings
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Re: Focus Fine Tune
In reply to richiebee, 5 months ago

richiebee wrote:

Interesting. The implication here and the suggestion in others posts is that this is somehow semi-destructive. On my camera, all lenses start with a value of zero, and you can offset each lens (which gets recognized by the camera when its attached) using a single parameter slider. Resetting the value to zero for each lens (or I suspect resetting the camera itself will put all lenses back to default) is all that is needed to return it to its original position so I don't get the need to be so careful here. You're not taking a screwdriver to anything.

Is it done differently on other cameras?

R.

ajscullard wrote:

As darklamp says, unless you really know what you are doing and you have sufficient experience to analyse your results well enough to ascertain correctly why a shot is not sharp enough, then you need to think carefully about dong any MA. You may end up making things worse so be sure you have some way of resetting the lens(es) to the original settings.

So here's my take on the subject. Darklamp is correct that properly setting the AFFT coefficents requires patience, thoroughness, and the right setup.  It doesn't help that there are sites on the web that purport to help but use wrongly designed targets (the infamous 45 degree piece of paper) that can induce further errors.  It also is a process that requires really a statistical approach to get absolutely right, because there's an inherent spread to the results that is a function of lighting level, type of target, and where the lens was focused previously.  You need to test multiple times at each AFFT coefficient value and at each FL you plan to use. So we're talking 50-100 measurements per FL. Oh, and it needs to be on tripod, with careful attention to the orthonormality of the target and optical axis, and sources of vibration need to be carefully removed; i.e., make sure that there's a goodly delay between mirror-up and shutter release.  Then you get to process the results and see where the statistics take you.

AFFT is not useless for zooms, but if you only have a single AFFT coefficient per lens, you're definitely going to have to compromise or optimize at a particular FL. Some manufacturers provide 2 or more AFFT coefficents and an interpolation feature, allowing you to at least approximate the full focal-plane vs. focal-length curve.  But most don't.  AFFT works most completely with primes, but then only if they're at the correct subject-camera distance.  AF error is not constant with subject-camera distance but asymptotes as you increase distance.

That being said, AFFT is commonplace on Pro bodies because pros demand the best focusing performance and know how to calibrate it.  It is becoming more common on lower end bodies both as a marketing feature differentiation but also because the high resolution of current bodies will reveal focusing errors more readily, and because manufacturing QC standards are permitting more variability in lens and body performance.  It is true that slower lenses with their greater minimum depth of field are more tolerant of focusing errors than fast lenses, so as long as you're using an f4-f5.6 kit lens not having AFFT is a reasonable thing; but when you put that cheapo (and good) 35mm f1.8 on it, you might start seeing things.

Where I have found AFFT useful on my D7100 is in using telezooms. The 70-300 Nikon is not as sharp as I might like it at 300mm, but that's where one tends to use telezooms, and mine, for example had a +9 correction at 300mm but a +3 correction at 70mm.  In this case, I'd use +9, and I will see differences in sharpness when I do so, even handheld, but again with as many sources of vibration as possible eliminated.  My midrange zoom, on the other hand, is more problematic. There, I have to use an average value.

How long did it take me to set my lenses up? About a day (a bright, sunny day), and FoCal, and 300+ measurements. At least I won't have to send my lens and body back to Nikon Service for basic lens-body matching (which they actually don't do, they just calibrate the lens and body separately to the centers of their individual specifications to allow for the maximum number of lens-body combinations). But if there's something seriously wrong with the body AF or the lens calibration, the factory calibration uses far more parameters than are available to the AFFT user - far more even than Sigma does with its USB dock and lens tuning program.

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stevo23
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Re: Focus Fine Tune
In reply to mosswings, 5 months ago

mosswings wrote:

richiebee wrote:

Interesting. The implication here and the suggestion in others posts is that this is somehow semi-destructive. On my camera, all lenses start with a value of zero, and you can offset each lens (which gets recognized by the camera when its attached) using a single parameter slider. Resetting the value to zero for each lens (or I suspect resetting the camera itself will put all lenses back to default) is all that is needed to return it to its original position so I don't get the need to be so careful here. You're not taking a screwdriver to anything.

Is it done differently on other cameras?

R.

ajscullard wrote:

As darklamp says, unless you really know what you are doing and you have sufficient experience to analyse your results well enough to ascertain correctly why a shot is not sharp enough, then you need to think carefully about dong any MA. You may end up making things worse so be sure you have some way of resetting the lens(es) to the original settings.

So here's my take on the subject. Darklamp is correct that properly setting the AFFT coefficents requires patience, thoroughness, and the right setup. It doesn't help that there are sites on the web that purport to help but use wrongly designed targets (the infamous 45 degree piece of paper) that can induce further errors. It also is a process that requires really a statistical approach to get absolutely right, because there's an inherent spread to the results that is a function of lighting level, type of target, and where the lens was focused previously. You need to test multiple times at each AFFT coefficient value and at each FL you plan to use. So we're talking 50-100 measurements per FL. Oh, and it needs to be on tripod, with careful attention to the orthonormality of the target and optical axis, and sources of vibration need to be carefully removed; i.e., make sure that there's a goodly delay between mirror-up and shutter release. Then you get to process the results and see where the statistics take you.

AFFT is not useless for zooms, but if you only have a single AFFT coefficient per lens, you're definitely going to have to compromise or optimize at a particular FL. Some manufacturers provide 2 or more AFFT coefficents and an interpolation feature, allowing you to at least approximate the full focal-plane vs. focal-length curve. But most don't. AFFT works most completely with primes, but then only if they're at the correct subject-camera distance. AF error is not constant with subject-camera distance but asymptotes as you increase distance.

That being said, AFFT is commonplace on Pro bodies because pros demand the best focusing performance and know how to calibrate it. It is becoming more common on lower end bodies both as a marketing feature differentiation but also because the high resolution of current bodies will reveal focusing errors more readily, and because manufacturing QC standards are permitting more variability in lens and body performance. It is true that slower lenses with their greater minimum depth of field are more tolerant of focusing errors than fast lenses, so as long as you're using an f4-f5.6 kit lens not having AFFT is a reasonable thing; but when you put that cheapo (and good) 35mm f1.8 on it, you might start seeing things.

Where I have found AFFT useful on my D7100 is in using telezooms. The 70-300 Nikon is not as sharp as I might like it at 300mm, but that's where one tends to use telezooms, and mine, for example had a +9 correction at 300mm but a +3 correction at 70mm. In this case, I'd use +9, and I will see differences in sharpness when I do so, even handheld, but again with as many sources of vibration as possible eliminated. My midrange zoom, on the other hand, is more problematic. There, I have to use an average value.

How long did it take me to set my lenses up? About a day (a bright, sunny day), and FoCal, and 300+ measurements. At least I won't have to send my lens and body back to Nikon Service for basic lens-body matching (which they actually don't do, they just calibrate the lens and body separately to the centers of their individual specifications to allow for the maximum number of lens-body combinations). But if there's something seriously wrong with the body AF or the lens calibration, the factory calibration uses far more parameters than are available to the AFFT user - far more even than Sigma does with its USB dock and lens tuning program.

I don't find it to be all that difficult or complex as you describe. I've managed to find critical focus fine tuning for a given lens in an hour or so. It's a lot of shooting and re-shooting to get it right, but if it takes a whole day, I think something else is wrong. Seriously, it's not and can't be a perfect science because lenses don't behave linearly.

I also think flat targets are useless. 3 dimensional subjects are best as that's what we shoot. Trying to determine focus from a flat, black and white target won't tell you what the lens will do in real life. You need all the colors and all three dimensions as that is what your lens will be seeing when you shoot a photo.

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mosswings
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Re: Focus Fine Tune
In reply to stevo23, 5 months ago

stevo23 wrote:

I don't find it to be all that difficult or complex as you describe. I've managed to find critical focus fine tuning for a given lens in an hour or so. It's a lot of shooting and re-shooting to get it right, but if it takes a whole day, I think something else is wrong. Seriously, it's not and can't be a perfect science because lenses don't behave linearly.

I also think flat targets are useless. 3 dimensional subjects are best as that's what we shoot. Trying to determine focus from a flat, black and white target won't tell you what the lens will do in real life. You need all the colors and all three dimensions as that is what your lens will be seeing when you shoot a photo.

And therein lies the problem with AFFT. Manufacturers use flat targets for their calibrations, but utilize color in their focusing algorithms. 3-D targets are what we focus on, but what the camera actually does is come up with what it thinks is the focal point based on striking an average across the focus zone used. And that might not be what we thought we were focusing on.  But starting with the flat target gets you quite close, and then you can tweak from there.

Admittedly, I was calibrating 4 lenses: 3 zooms, 1 prime, and FoCal is a statistical analyzer, and I was being anal retentive because I wanted to see the AF tuning spreads as well as get an AFFT coefficient. You can use DotTune or any of the other camera-based methods, and if you're using a Canon instead of the Nikon I am using, you have the wonderful advantage of fully automating the calibration process. Nikon doesn't give 3rd parties access to its camera control firmware like Canon does.  But even with all that, I spent a couple of hours per lens.  So not that far off from your hour or so.

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EinsteinsGhost
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Re: Focus Fine Tune
In reply to mosswings, 5 months ago

stevo23 wrote:

I don't find it to be all that difficult or complex as you describe. I've managed to find critical focus fine tuning for a given lens in an hour or so. It's a lot of shooting and re-shooting to get it right, but if it takes a whole day, I think something else is wrong. Seriously, it's not and can't be a perfect science because lenses don't behave linearly.

I also think flat targets are useless. 3 dimensional subjects are best as that's what we shoot. Trying to determine focus from a flat, black and white target won't tell you what the lens will do in real life. You need all the colors and all three dimensions as that is what your lens will be seeing when you shoot a photo.

And therein lies the problem with AFFT. Manufacturers use flat targets for their calibrations, but utilize color in their focusing algorithms. 3-D targets are what we focus on, but what the camera actually does is come up with what it thinks is the focal point based on striking an average across the focus zone used. And that might not be what we thought we were focusing on. But starting with the flat target gets you quite close, and then you can tweak from there.

Admittedly, I was calibrating 4 lenses: 3 zooms, 1 prime, and FoCal is a statistical analyzer, and I was being anal retentive because I wanted to see the AF tuning spreads as well as get an AFFT coefficient. You can use DotTune or any of the other camera-based methods, and if you're using a Canon instead of the Nikon I am using, you have the wonderful advantage of fully automating the calibration process. Nikon doesn't give 3rd parties access to its camera control firmware like Canon does. But even with all that, I spent a couple of hours per lens. So not that far off from your hour or so.

Its not that complicated. And it doesn't have to be a 1.8 (fast) lens either. Case in point: Minolta 24-50/4. This mid 80s lens required MFA when I noticed backfocus on my Sony NEX. It didn't take long to figure out that at 24-28mm, the lens wasn't focusing where I wanted it to. A simple adjustment and now a non issue, at either end or in between. The camera/adapter remembers the lens, so put it on and go shooting with precise AF.

Not having access to MFA would have rendered the lens pretty useless except with MF. The first thing with any newly received lens I do is a basic test of focus (If it is AF, or infinity focus if it is manual lens with adapter).

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