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Archive 2013 · DotTune: New AF tune technique, no photos required

  
 
gpelpel
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p.10 #1 · p.10 #1 · DotTune: New AF tune technique, no photos required


I don't really understand why you would need fine tuning at infinity. The DOF is so wide at infinity that fine tuning won't have much, or any, impact.
My understanding is that fine tuning is critical when we are woking with shallow DOF so tuning the lens wide open at a relatively short distance subject seems the most helpful.



Mar 01, 2016 at 03:59 PM
CanadaMark
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p.10 #2 · p.10 #2 · DotTune: New AF tune technique, no photos required


mco_970 wrote:
I am really interested to see what they did on the D500 to automate the process. The Sigma dock was time consuming, but the results look good. I would be happy not to ever tune another zoom, though.



From what we know so far (which isn't everything), I am pretty sure it just automates the discovery of a single value. A step forward, but nothing mind blowing. In my opinion, this will simply be most helpful in determining if you should exchange a newly purchased lens or not, especially for zooms. Simply run the Auto AF fine tune at a variety of combinations and if the camera spits out a value above whatever tolerance threshold you determine at any given combination, you exchange the lens. It will just speed up the process many people already do to check their lenses for AF issues, and save you lots of time trying to make compromises with zooms. Mostly I see it just saving time when checking a lens, it won't actually be any more valuable as far as implementation goes unless they surprise everyone with storage values for multiple combinations of FL and distance.



Mar 01, 2016 at 04:07 PM
snapsy
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p.10 #3 · p.10 #3 · DotTune: New AF tune technique, no photos required


gpelpel wrote:
I don't really understand why you would need fine tuning at infinity. The DOF is so wide at infinity that fine tuning won't have much, or any, impact.
My understanding is that fine tuning is critical when we are woking with shallow DOF so tuning the lens wide open at a relatively short distance subject seems the most helpful.


There are a few factors. The optical aberrations in a lens that can contribute to the need for AFMA may vary depending on focus position and may not be linear between MFD and infinity. Also, depth-of-focus (at image plane) is more important than depth-of-field when determining acceptable focus variability. Lastly, empirical evidence demonstrates that focusing at mid-to-infinity distances at large apertures is much more prone to accuracy and precision errors than at nearer distances and MFD. This may be partly due to the coarseness of discrete focus positions in the lens as you move toward infinity (ie, more discrete focus steps at MFD than infinity)...although this relationship to AFMA isn't clear cut to me. But you can measure this yourself with most fast primes - they'll be much less precise at infinity than they will be at closer distances.



Mar 01, 2016 at 04:42 PM
snapsy
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p.10 #4 · p.10 #4 · DotTune: New AF tune technique, no photos required


The D5 Menu Guid Manual lists the following instructions on page 110 for Nikon's new auto AF tune feature of the D5/D500, which based on details available elsewhere appears to operate the same as an automated version of DotTune.

Auto Fine-Tuning
Auto fine-tuning is available in live view. After mounting the camera on a tripod and selecting maximum aperture (recommended), rotating the live view selector to [Camera], selecting single-servo autofocus (AF-S), setting the AF-area mode to wide-or-normal-area AF, selecting the center focus point, and if possible engaging focus zoom for accurate focus, focus the camera and then press the AF-mode and movie-record buttons until instructions are displayed (you will need to press the buttons for a little over 2 seconds). Highlight Yes and press (OK) to add the new value to the saved values list.



Mar 23, 2016 at 03:16 PM
binary visions
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p.10 #5 · p.10 #5 · DotTune: New AF tune technique, no photos required


That's really pretty awesome when you consider how fast it becomes to quickly check a lens for accuracy or do a fast tune for a particular shooting situation.

Why this wasn't in there a few years ago is silly given its simplicity, but it's nice to see it now.



Mar 23, 2016 at 04:04 PM
Mark_L
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p.10 #6 · p.10 #6 · DotTune: New AF tune technique, no photos required


snapsy wrote:
The D5 Menu Guid Manual lists the following instructions on page 110 for Nikon's new auto AF tune feature of the D5/D500, which based on details available elsewhere appears to operate the same as an automated version of DotTune.

Auto Fine-Tuning
Auto fine-tuning is available in live view. After mounting the camera on a tripod and selecting maximum aperture (recommended), rotating the live view selector to [Camera], selecting single-servo autofocus (AF-S), setting the AF-area mode to wide-or-normal-area AF, selecting the center focus point, and if possible engaging focus zoom for accurate focus, focus the camera and then press the AF-mode and movie-record
...Show more

It doesn't sound like it is very automated but I remain open to being convinced. Still no way to fine tune at different distances - just a crude offset.

Why the heck lenses (and bodies) can't be profiled on testing and the values written to firmware I'll never know. /rant



Mar 23, 2016 at 05:03 PM
CanadaMark
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p.10 #7 · p.10 #7 · DotTune: New AF tune technique, no photos required


Mark_L wrote:
It doesn't sound like it is very automated but I remain open to being convinced. Still no way to fine tune at different distances - just a crude offset.

Why the heck lenses (and bodies) can't be profiled on testing and the values written to firmware I'll never know. /rant


The fine-tune process itself is automated now, however you are correct that it still only arrives at a single value and therefore a single combination of subject distance and focal length, so it's pretty useless for most applications and especially with a zoom lens. Where I see it being useful is for is very quickly telling you if you need to exchange the lens you just bought, by giving easily attainable numerical values at a variety of data points to see if your lens is out of tune. They are still including the usual disclaimer alongside the AF Fine tune description in the manual:."AF tuning is not recommended in most situations and may interfere with normal focus; use only when required"

Like I was saying before, I think lens returns/exchanges are going to go way up now that people have an easy to understand numerical value provided by the camera itself which tells them if their lens is out of tune at any given FL/distance combination. "My camera says my lens is out of tune by +15 at 100mm and -5 at 200mm, I'd like to exchange please".

On the flip side, you no longer have to check PDAF vs CDAF manually when you get a new lens - you simply run auto AF fine tune at a variety of FL/distance combinations and if every returned value is around zero, you're good to go. It'll save a bit of time but it's far from a miracle solution in my opinion.



Mar 23, 2016 at 05:18 PM
rw11
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p.10 #8 · p.10 #8 · DotTune: New AF tune technique, no photos required


maybe if lens returns/exchanges go way up, we'll get manf.s to do a better job...


Mar 23, 2016 at 05:57 PM
Mark_L
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p.10 #9 · p.10 #9 · DotTune: New AF tune technique, no photos required


CanadaMark wrote:
The fine-tune process itself is automated now, however you are correct that it still only arrives at a single value and therefore a single combination of subject distance and focal length, so it's pretty useless for most applications and especially with a zoom lens.


Ah, I read "follow the on screen instructions" type line as having to do all sorts of monkeying around.

I really do hope there are loads of returns for non-linear focus performance with distance/zoom. Perhaps this is why it has taken so long to implement but they've caved under pressure. Retails may be the ones the feel it though, Nikon may well invoke the "fine tuning may affect normal af performance" line somehow.



Mar 24, 2016 at 05:36 AM
Artscar2
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p.10 #10 · p.10 #10 · DotTune: New AF tune technique, no photos required


Tag for reference (late to the party)



Mar 24, 2016 at 01:54 PM
BSPhotog
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p.10 #11 · p.10 #11 · DotTune: New AF tune technique, no photos required


Just tried this for the first time with my 85mm f/1.4D and 50mm f/1.4D on d600 and D800. Huge improvement, thanks!


Jun 07, 2016 at 08:57 AM
Korben
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p.10 #12 · p.10 #12 · DotTune: New AF tune technique, no photos required


Just a quick question, is it normal for the AF fine tuning values to change just by turning the camera off and on? I explain: I do the tuning as indicated, and say I get +4 / -19, the calculator says "-7.5 (Use -7 or -8)". Turn the camera off, do a tuning again and I get +5 / -18, "-6.5 (Use -6 or -7)". So there's already a variation there. I do the tuning again a few days later and I get, "Use -3" or something else. Is this swaying back and forth between values common?


Jun 21, 2016 at 09:31 AM
CanadaMark
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p.10 #13 · p.10 #13 · DotTune: New AF tune technique, no photos required


Korben wrote:
Just a quick question, is it normal for the AF fine tuning values to change just by turning the camera off and on? I explain: I do the tuning as indicated, and say I get +4 / -19, the calculator says "-7.5 (Use -7 or -8)". Turn the camera off, do a tuning again and I get +5 / -18, "-6.5 (Use -6 or -7)". So there's already a variation there. I do the tuning again a few days later and I get, "Use -3" or something else. Is this swaying back and forth between values common?


This method of tuning is not precise. I wouldn't be surprised if you got different results every time you did it. Also keep in mind a difference of one or two points is quite minimal, and likely within the tolerances of the AF system and lens AF. For example if I thought a lens needed +1, I would leave it at zero because it probably doesn't actually need any tune.

If your lens was out as high as -19 at any combination of focal length and subject distance I would be exchanging that lens instead of pulling your hair out trying to get a single AFFT value that works at all combinations, which you probably won't. Also when you set a value, you then need to test it at every other combination of subject distance and focal length to make sure you didn't make it worse elsewhere (which you probably did). I know I sound like a broken record but Nikon's implementation of AFFT is a band aid at best, and only if you are very, very lucky will you find a value that zeros your lens at what can be dozens of combinations of distance and FL. IMHO you are far better off exchanging the lens if that is still an option.



Jun 21, 2016 at 10:33 AM
snapsy
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p.10 #14 · p.10 #14 · DotTune: New AF tune technique, no photos required


CanadaMark wrote:
This method of tuning is not precise. I wouldn't be surprised if you got different results every time you did it. Also keep in mind a difference of one or two points is quite minimal, and likely within the tolerances of the AF system and lens AF. For example if I thought a lens needed +1, I would leave it at zero because it probably doesn't actually need any tune.

If your lens was out as high as -19 at any combination of focal length and subject distance I would be exchanging that lens instead of pulling your hair out trying
...Show more

You post this same incorrcect information to every tuning thread. The fact is AFMA is very precise and thousands of photographers have used it successfully. Additionally, Nikon uses the same mechanism as DotTune in their new automated AFMA mechanism in the D5/D500, which is very precise if you perform their function multiple times on the same locked focus and average the results. This multiple invocation is required because Nikon's automated implementation doesn't perform the multiple phase-detect cycles that are part of the DotTune procedure.

Korben, the reason you're likely getting different midpoint values for each test is due to variation of your focus step. For optimal results I would suggest either manually focusing in LV at 100% magnification using an optical loupe or using a target with 3D references for precise focusing. This is because Nikon's implementation of contrast-detect AF in LV is not very precise. Another thing you can try is to perform multiple DotTune operations on the same locked focus, which will eliminate focus variability from the equation and establish how good your target, lighting, and your viewfinder confirmation evaluation is.



Jun 21, 2016 at 11:08 AM
Korben
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p.10 #15 · p.10 #15 · DotTune: New AF tune technique, no photos required


Thanks, I can try manual focus in LV but my eyes are not what they used to be and I'm not sure if the results would be even worse. What do you mean by 3D references? I'm using the chart that was mentioned in the video, it's just a bunch of criss-crossed lines. One more thing: does it make any difference what AF area mode you use? Auto, single, group... and if you use center, spot or matrix mode?

Thanks!



Jun 21, 2016 at 11:36 AM
CanadaMark
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p.10 #16 · p.10 #16 · DotTune: New AF tune technique, no photos required


snapsy wrote:
You post this same incorrcect information to every tuning thread. The fact is AFMA is very precise and thousands of photographers have used it successfully. Additionally, Nikon uses the same mechanism as DotTune in their new automated AFMA mechanism in the D5/D500, which is very precise if you perform their function multiple times on the same locked focus and average the results. This multiple invocation is required because Nikon's automated implementation doesn't perform the multiple phase-detect cycles that are part of the DotTune procedure.

Korben, the reason you're likely getting different midpoint values for each test is due to variation
...Show more

You are misunderstanding me I think. He's getting a value of -19 on one end, and +4 at the other - using a midpoint of -7 or -8 is nowhere near precise. The only precise way to do it is currently impossible, which would involve a separate value for every combination of FL and distance. Nikon's automated implementation does not solve the problem either except for a single data set. If you have to max out AFFT to fix your lens at any combination, you should be exchanging it because you will never zero it out across the entire range. Further, if you have to settle on some middle-ground value that makes your lens OK everywhere but never great, that's not a proper solution either. Viewfinder 'tuning' has been around since the D3 in 2007 and it has the same problems today as it did back then. Until Nikon opens up more data points, you're always going to be better off exchanging the lens for one that requires no AFFT. Sigma has the right idea with the dock, but even that is an extremely painful process.



Jun 21, 2016 at 12:50 PM
snapsy
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p.10 #17 · p.10 #17 · DotTune: New AF tune technique, no photos required


CanadaMark wrote:
You are misunderstanding me I think. He's getting a value of -19 on one end, and +4 at the other - using a midpoint of -7 or -8 is nowhere near precise.

I understand you and you're incorrect. The phase detection feedback provided by Nikon bodies via the rangefinder is a continuum of phase measurement values. The fringe of AFMA values that yield a solid confirmation represent the the largest measured phase differential for which the camera still believes produces relatively sharp photos. The purpose of having a range rather than an abrupt single value is to make manual focusing to the rangefinder easier; this is also why the range of confirmed values grows about about 2.5x when the camera or lens is in MF mode, again to make it easier to bring the lens quickly into near focus. Since the range of confirmed values (both +/-) represents a continuum of phase measurement values, the midpoint of that range represents the optimal AFMA value. The absolute size of the range has no bearing on the accuracy of the midpoint - it's simply a function of the focal length and maximum aperture of the lens. For Nikon's AFMA in the D5/D500, using the full confirmed range is not necessary since the camera is not required to provide relative feedback like it does in the rangefinder - instead the camera simply selects the AFMA value with the minimal phase detection differential, which yields the same result as the midpoint of the confirmed range used by DotTune.

CanadaMark wrote:
The only precise way to do it is currently impossible, which would involve a separate value for every combination of FL and distance. Nikon's automated implementation does not solve the problem either except for a single data set. If you have to max out AFFT to fix your lens at any combination, you should be exchanging it because you will never zero it out across the entire range. Further, if you have to settle on some middle-ground value that makes your lens OK everywhere but never great, that's not a proper solution either. Viewfinder 'tuning' has been around since the
...Show more

You're conflating the frequency of distance-specific AFMA variation with the underlying usefulness of the mechanism itself. I've tuned 30 lenses across 10 Nikon bodies and of those only 3 produced material distance-specific variation, and two of those were third-party bodies (Sigma ART 35mm and 50mm, both of which were correctable using Sigma's dock).



Jun 21, 2016 at 01:08 PM
snapsy
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p.10 #18 · p.10 #18 · DotTune: New AF tune technique, no photos required


Korben wrote:
Thanks, I can try manual focus in LV but my eyes are not what they used to be and I'm not sure if the results would be even worse. What do you mean by 3D references? I'm using the chart that was mentioned in the video, it's just a bunch of criss-crossed lines. One more thing: does it make any difference what AF area mode you use? Auto, single, group... and if you use center, spot or matrix mode?

Thanks!


By 3D reference I mean something placed in front and behind of the target so that you have cues for more precise focusing within the DOF. When you focus on a 2D target there is a range of focus positions that will yield that target in apparent focus due to the DOF for that focus distance and aperture. Even though each of those focus positions will appear optimal, you'll be shifting where you are in terms of the precise focus point, sometimes shifting the DOF slightly away and sometimes toward the camera. Using a 3D target like a LensAlign will allow you to precisely set where the focus is within the DOF envelope. In practice you usually don't need this level of precision when tuning most lenses but there may be outliers that require more precision.

Focusing mode shouldn't matter but I definitely recommend single AF point in AF-S point, using the center point.



Jun 21, 2016 at 01:15 PM
Korben
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p.10 #19 · p.10 #19 · DotTune: New AF tune technique, no photos required


Thanks a lot for the information! One more oddity: with the camera still firmly on the tripod since I left it this morning, I did a new tuning with AF-S/single/center point and now the values are +1 / -9 instead of +5 / -18. The range is wild, something doesn't make sense, either I'm doing something wrong or the lens/camera combo is out of whack. Any ideas?


Jun 21, 2016 at 01:36 PM
CanadaMark
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p.10 #20 · p.10 #20 · DotTune: New AF tune technique, no photos required


snapsy wrote:
I understand you and you're incorrect. The phase detection feedback provided by Nikon bodies via the rangefinder is a continuum of phase measurement values. The fringe of AFMA values that yield a solid confirmation represent the the largest measured phase differential for which the camera still believes produces relatively sharp photos. The purpose of having a range rather than an abrupt single value is to make manual focusing to the rangefinder easier; this is also why the range of confirmed values grows about about 2.5x when the camera or lens is in MF mode, again to make it easier to
...Show more

We will have to agree to disagree, and I still don't think you understand what I am saying based on your response. Nikon strongly cautions the method as well. Your experience is very different than mine, I don't think we will gain anything from arguing. If you are satisfied with this method then that's great and I'll leave it at that, but some of the things you are telling people are misleading.



Jun 21, 2016 at 02:25 PM
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