D5 auto AF fine-tune: User notes

Started Apr 26, 2016 | Discussions
Marianne Oelund Veteran Member • Posts: 7,779
D5 auto AF fine-tune: User notes
32

After experimenting with this new feature for a while, I've found some issues and characteristics that I thought would be worth sharing.  Here is a guide for use of the feature, with some basics about how it operates.

Before starting, you want to make sure you have the center AF point selected if using a phase-detect AF mode which takes a user-selected point; the feature requires this, and will only allow auto-calibration of that one point.  Set the camera up on a tripod, aimed at a suitable AF target with good lighting.  The auto AF fine tune feature will not operate under dim lighting (under LV 5 or so) even though AF is rated down to LV -4.

Engage Live View and make sure the LV focus mode is set to AF-S and Wide or Normal single-point.  You also need to make sure the LV focus position is at center.  Now for the critical part:  Carefully focus the lens so it is precisely focused on the subject at the center AF point.  If you have a good target, using LV AF may be sufficient, but you should still check at high magnification, preferably with a slant-ruler in the image to help judge the precise focus plane.  Auto AF fine-tune will use this lens focus position as its reference, so if the focus is slightly off, so will the automatic fine tune adjustment be!

Hold down the AF-mode select button (on the AF-M switch next to the lens mount) and the video-record button simultaneously for several seconds.  This should bring up the dialog box "Before proceeding, fix the camera in place and check that it is focused.  Proceed?" with Yes and No options.

[Note:  If any of the AF settings listed above are not correct, you will see an error message "Auto AF fine tune is not available at current focus settings."  However, there is a potential alignment issue, and sometimes you will get this error message even when everything appears set correctly.  To proceed in this case, exit LV, move the AF point away from center, then back to center, and return to LV.  This realigns the LV AF point as needed.]

Press OK to initiate the process.  The camera will exit LV, operate the phase-detect AF system to measure any focus error that it believes is present, then calculate the required offset (fine tune value) to correct that error.  Finally, the fine tune value is entered into the internal table for that lens, and a completion dialog box is displayed.  Press OK to confirm; you may then look at the AF fine tune menu item to see the new value that the camera calculated.

If there was not sufficient light, or if the lens requires a fine tune value beyond the -20 to +20 range, the error message "Auto AF fine tune failed." is displayed.  Note that this could be caused by the lens focus being accidentally disturbed, so you may want to try repeating the process.

It is important to understand that due to the fickle nature of phase-detect AF, the calculated fine-tune value may not be optimal.  I recommend repeating the procedure at least half a dozen times (if not 10 or more) to establish the range of values that can result.  Then, manually select a value in the center of the range.  This means, of course, that the complete process is not so quick, and you may prefer to use manual AF fine tune methods instead.

AF target quality

By repeating the process a number of times, you will obtain a range of values which will give some guidance regarding the suitability of your AF target.  A good target can produce a range of fine-tune values which differ by only 5 to 6 from lowest to highest.  Less suitable targets may produce a much larger range of values, and may even produce distributions of values that are end-weighted rather than center-weighted as you would normally expect.

Some good targets I've found are bar-code strips, or printed block letters on a highly contrasting background, sized so just a few characters will fit within the AF point.

I will continue to do some work evaluating AF targets, and post again if I make any noteworthy discoveries.

Interestingly, I have not found a correlation between light level and the consistency of auto AF fine tune.  Provided the lighting is sufficient (about LV 5 or higher) to allow the feature to work, increasing the illumination does not appear to help.

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- Marianne

Nikon D5
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Leonard Shepherd
Leonard Shepherd Forum Pro • Posts: 17,765
Re: D5 auto AF fine-tune: User notes

Marianne Oelund wrote:

AF target quality

By repeating the process a number of times, you will obtain a range of values which will give some guidance regarding the suitability of your AF target. A good target can produce a range of fine-tune values which differ by only 5 to 6 from lowest to highest. Less suitable targets may produce a much larger range of values, and may even produce distributions of values that are end-weighted rather than center-weighted as you would normally expect.

Some good targets I've found are bar-code strips, or printed block letters on a highly contrasting background, sized so just a few characters will fit within the AF point.

I will continue to do some work evaluating AF targets, and post again if I make any noteworthy discoveries.

Interestingly, I have not found a correlation between light level and the consistency of auto AF fine tune. Provided the lighting is sufficient (about LV 5 or higher) to allow the feature to work, increasing the illumination does not appear to help.

When you provide more information it could be useful to comment on what Nikon imply are more reliable subjects for PD AF.

One reason for asking is, in the pre release publicity implied a less than 100% accurate translation

"Auto AF fine-tune example

The auto fine-tuning sample operation (shown right) uses an AF-S NIKKOR 600mm f/4E FL ED VR lens, with a 24 cm × 24 cm/9.4 in. × 9.4 in. Nikon brand-logo wall panel as the subject. During live view, focus is achieved after creating sufficient focus distance and confirming that the subject appears at an appropriate size. The ideal subject is a flat object with color contrast. One criterion for the focus distance is whether it frames a bust shot of a portrait subject with the particular lens in use."

The sample implied a single black and white edge which Nikon has cautioned with previous DSLR models might cause focus error.

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Leonard Shepherd
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sgoldswo
sgoldswo Veteran Member • Posts: 5,725
Re: D5 auto AF fine-tune: User notes
1

Marianne, Thank you for this detailed note - very useful knowhow.

Marianne Oelund wrote:

After experimenting with this new feature for a while, I've found some issues and characteristics that I thought would be worth sharing. Here is a guide for use of the feature, with some basics about how it operates.

Before starting, you want to make sure you have the center AF point selected if using a phase-detect AF mode which takes a user-selected point; the feature requires this, and will only allow auto-calibration of that one point. Set the camera up on a tripod, aimed at a suitable AF target with good lighting. The auto AF fine tune feature will not operate under dim lighting (under LV 5 or so) even though AF is rated down to LV -4.

Engage Live View and make sure the LV focus mode is set to AF-S and Wide or Normal single-point. You also need to make sure the LV focus position is at center. Now for the critical part: Carefully focus the lens so it is precisely focused on the subject at the center AF point. If you have a good target, using LV AF may be sufficient, but you should still check at high magnification, preferably with a slant-ruler in the image to help judge the precise focus plane. Auto AF fine-tune will use this lens focus position as its reference, so if the focus is slightly off, so will the automatic fine tune adjustment be!

Hold down the AF-mode select button (on the AF-M switch next to the lens mount) and the video-record button simultaneously for several seconds. This should bring up the dialog box "Before proceeding, fix the camera in place and check that it is focused. Proceed?" with Yes and No options.

[Note: If any of the AF settings listed above are not correct, you will see an error message "Auto AF fine tune is not available at current focus settings." However, there is a potential alignment issue, and sometimes you will get this error message even when everything appears set correctly. To proceed in this case, exit LV, move the AF point away from center, then back to center, and return to LV. This realigns the LV AF point as needed.]

Press OK to initiate the process. The camera will exit LV, operate the phase-detect AF system to measure any focus error that it believes is present, then calculate the required offset (fine tune value) to correct that error. Finally, the fine tune value is entered into the internal table for that lens, and a completion dialog box is displayed. Press OK to confirm; you may then look at the AF fine tune menu item to see the new value that the camera calculated.

If there was not sufficient light, or if the lens requires a fine tune value beyond the -20 to +20 range, the error message "Auto AF fine tune failed." is displayed. Note that this could be caused by the lens focus being accidentally disturbed, so you may want to try repeating the process.

It is important to understand that due to the fickle nature of phase-detect AF, the calculated fine-tune value may not be optimal. I recommend repeating the procedure at least half a dozen times (if not 10 or more) to establish the range of values that can result. Then, manually select a value in the center of the range. This means, of course, that the complete process is not so quick, and you may prefer to use manual AF fine tune methods instead.

AF target quality

By repeating the process a number of times, you will obtain a range of values which will give some guidance regarding the suitability of your AF target. A good target can produce a range of fine-tune values which differ by only 5 to 6 from lowest to highest. Less suitable targets may produce a much larger range of values, and may even produce distributions of values that are end-weighted rather than center-weighted as you would normally expect.

Some good targets I've found are bar-code strips, or printed block letters on a highly contrasting background, sized so just a few characters will fit within the AF point.

I will continue to do some work evaluating AF targets, and post again if I make any noteworthy discoveries.

Interestingly, I have not found a correlation between light level and the consistency of auto AF fine tune. Provided the lighting is sufficient (about LV 5 or higher) to allow the feature to work, increasing the illumination does not appear to help.

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Antal I Kozma Senior Member • Posts: 2,900
Re: D5 auto AF fine-tune: User notes
2

Very much appreciated.

Best, AIK

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lickity split
lickity split Veteran Member • Posts: 5,431
Re: D5 auto AF fine-tune: User notes

Marianne Oelund wrote:

After experimenting with this new feature for a while, I've found some issues and characteristics that I thought would be worth sharing. Here is a guide for use of the feature, with some basics about how it operates.

Before starting, you want to make sure you have the center AF point selected if using a phase-detect AF mode which takes a user-selected point; the feature requires this, and will only allow auto-calibration of that one point. Set the camera up on a tripod, aimed at a suitable AF target with good lighting. The auto AF fine tune feature will not operate under dim lighting (under LV 5 or so) even though AF is rated down to LV -4.

Engage Live View and make sure the LV focus mode is set to AF-S and Wide or Normal single-point. You also need to make sure the LV focus position is at center. Now for the critical part: Carefully focus the lens so it is precisely focused on the subject at the center AF point. If you have a good target, using LV AF may be sufficient, but you should still check at high magnification, preferably with a slant-ruler in the image to help judge the precise focus plane. Auto AF fine-tune will use this lens focus position as its reference, so if the focus is slightly off, so will the automatic fine tune adjustment be!

Hold down the AF-mode select button (on the AF-M switch next to the lens mount) and the video-record button simultaneously for several seconds. This should bring up the dialog box "Before proceeding, fix the camera in place and check that it is focused. Proceed?" with Yes and No options.

[Note: If any of the AF settings listed above are not correct, you will see an error message "Auto AF fine tune is not available at current focus settings." However, there is a potential alignment issue, and sometimes you will get this error message even when everything appears set correctly. To proceed in this case, exit LV, move the AF point away from center, then back to center, and return to LV. This realigns the LV AF point as needed.]

Press OK to initiate the process. The camera will exit LV, operate the phase-detect AF system to measure any focus error that it believes is present, then calculate the required offset (fine tune value) to correct that error. Finally, the fine tune value is entered into the internal table for that lens, and a completion dialog box is displayed. Press OK to confirm; you may then look at the AF fine tune menu item to see the new value that the camera calculated.

If there was not sufficient light, or if the lens requires a fine tune value beyond the -20 to +20 range, the error message "Auto AF fine tune failed." is displayed. Note that this could be caused by the lens focus being accidentally disturbed, so you may want to try repeating the process.

It is important to understand that due to the fickle nature of phase-detect AF, the calculated fine-tune value may not be optimal. I recommend repeating the procedure at least half a dozen times (if not 10 or more) to establish the range of values that can result. Then, manually select a value in the center of the range. This means, of course, that the complete process is not so quick, and you may prefer to use manual AF fine tune methods instead.

AF target quality

By repeating the process a number of times, you will obtain a range of values which will give some guidance regarding the suitability of your AF target. A good target can produce a range of fine-tune values which differ by only 5 to 6 from lowest to highest. Less suitable targets may produce a much larger range of values, and may even produce distributions of values that are end-weighted rather than center-weighted as you would normally expect.

Some good targets I've found are bar-code strips, or printed block letters on a highly contrasting background, sized so just a few characters will fit within the AF point.

I will continue to do some work evaluating AF targets, and post again if I make any noteworthy discoveries.

Interestingly, I have not found a correlation between light level and the consistency of auto AF fine tune. Provided the lighting is sufficient (about LV 5 or higher) to allow the feature to work, increasing the illumination does not appear to help.

Good info here , that's pretty much what I did,I used a LensAlign target  and I also double checked Auto-AFFT with LensAlign just to be sure it was giving accurate #'s which in the beginning it wasn't but that was because of the light. The one thing I did that you didn't mention was in between each test (I did several)  I defocused . And I also zoomed in when I entered Liveview so the target filled the focus square then hit the AF-ON button.

An if I tested it 10 times 6 of those times I got the same # ,the other 4 times that number was either high or low a few points .  Majority rules.

Oh and mine was done on a D500 not D5

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OP Marianne Oelund Veteran Member • Posts: 7,779
Don't defocus/re-focus
3

lickity split wrote:

The one thing I did that you didn't mention was in between each test (I did several) I defocused . And I also zoomed in when I entered Liveview so the target filled the focus square then hit the AF-ON button.

Auto AF fine tune is a fundamentally different process than manually setting up fine tune, as it doesn't actually drive the lens focus group.  Instead, it just "reads" the focus error from the reference focus position that you establish (in Live View, using either contrast-detect AF or manual focusing).

You want to establish precise focus at the outset - just once - and then leave it there for all of the subsequent measurements via auto AF fine tune, otherwise you need to do the careful focus check all over again for each cycle.  Just be careful not to bump the lens focus ring or the AF-ON button (or shutter release if it activates AF) between the cycles.

Because the auto AF fine tune algorithm doesn't involve any movement of the lens focus elements, it gives more precise insight into the AF system's focus-error assessment by bypassing the mechanical variations in the lens focus drive which are involved in manual tuning.

And if I tested it 10 times 6 of those times I got the same # ,the other 4 times that number was either high or low a few points . Majority rules.

Sounds like you chose a good target.

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- Marianne

lickity split
lickity split Veteran Member • Posts: 5,431
Re: Don't defocus/re-focus
1

Marianne Oelund wrote:

lickity split wrote:

The one thing I did that you didn't mention was in between each test (I did several) I defocused . And I also zoomed in when I entered Liveview so the target filled the focus square then hit the AF-ON button.

Auto AF fine tune is a fundamentally different process than manually setting up fine tune, as it doesn't actually drive the lens focus group. Instead, it just "reads" the focus error from the reference focus position that you establish (in Live View, using either contrast-detect AF or manual focusing).

You want to establish precise focus at the outset - just once - and then leave it there for all of the subsequent measurements via auto AF fine tune, otherwise you need to do the careful focus check all over again for each cycle. Just be careful not to bump the lens focus ring or the AF-ON button (or shutter release if it activates AF) between the cycles.

Because the auto AF fine tune algorithm doesn't involve any movement of the lens focus elements, it gives more precise insight into the AF system's focus-error assessment by bypassing the mechanical variations in the lens focus drive which are involved in manual tuning.

And if I tested it 10 times 6 of those times I got the same # ,the other 4 times that number was either high or low a few points . Majority rules.

Sounds like you chose a good target.

When I say I defocused the lens I mean after I performed the test I saved the value I took a test shot using it via the viewfinder jotted the value down to average them all later then I erased the saved value defocused the lens and repeated the whole process over again and again and again.......

The one thing I didn't like about it is when your zoomed in while in Liveview even with being as gentle as possible you have to press the two buttons to start the test which makes the focus square dance around a bit . Not cool . They should have figured a way to trigger the process remotely via the ten pin and a menu setting.

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Tommi14 New Member • Posts: 6
Re: D5 auto AF fine-tune: User notes

In the earlier bodies, the range of the AF fine tune is different for the default adjustment and the lens specific adjustment. At least with my D700, setting the default value, for instance, to +10 has a larger effect than setting the lens specific value to +10. Marianne, what is your feeling, does the range of the auto AF fine tune in D5 correspond to the range of the default adjustment or the lens specific adjustment in the earlier bodies?

Regards,
Tommi

OP Marianne Oelund Veteran Member • Posts: 7,779
Test Sequence
2

lickity split wrote:

When I say I defocused the lens I mean after I performed the test I saved the value I took a test shot using it via the viewfinder jotted the value down to average them all later then I erased the saved value defocused the lens and repeated the whole process over again and again and again.......

Alright, but you are doing 5x as much work as you need to, and also injecting another variable into the process. By the way, you do not need to erase the saved value before starting again.

Here is an abbreviated sequence, starting after precise focus has been set in Live View:

1. Hold the AF-mode and video-record buttons until the dialog box is displayed.

2. Press OK - the test runs, taking only a fraction of a second.

3. Press OK again to confirm test completion.

4. Press Menu and look at the AF fine tune value that the camera wrote, then write it down.

5. If you want to continue, engage Live View and go to step 1.

The one thing I didn't like about it is when your zoomed in while in Liveview even with being as gentle as possible you have to press the two buttons to start the test which makes the focus square dance around a bit . Not cool . They should have figured a way to trigger the process remotely via the ten pin and a menu setting.

Pressing the AF-mode and video-record buttons simultaneously is not what starts the test. It only brings up the dialog box.

The test starts after you press OK when the dialog box is displayed.

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- Marianne

OP Marianne Oelund Veteran Member • Posts: 7,779
Fine tune range

Tommi14 wrote:

In the earlier bodies, the range of the AF fine tune is different for the default adjustment and the lens specific adjustment. At least with my D700, setting the default value, for instance, to +10 has a larger effect than setting the lens specific value to +10.

Yes, and this is what I found with all bodies I tested, prior to the D5.

Marianne, what is your feeling, does the range of the auto AF fine tune in D5 correspond to the range of the default adjustment or the lens specific adjustment in the earlier bodies?

My impression is that it is similar to the lens-specific adjustment of earlier bodies, but I need to make a careful check of this as it could well be different.  Thanks for asking.

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- Marianne

lickity split
lickity split Veteran Member • Posts: 5,431
Re: Test Sequence
1

Marianne Oelund wrote:

lickity split wrote:

When I say I defocused the lens I mean after I performed the test I saved the value I took a test shot using it via the viewfinder jotted the value down to average them all later then I erased the saved value defocused the lens and repeated the whole process over again and again and again.......

Alright, but you are doing 5x as much work as you need to, and also injecting another variable into the process. By the way, you do not need to erase the saved value before starting again.

OK I understand what your saying what your saying now the old saved value will just be written over by the new test and because the test is using Liveview and not the viewfinder the saved value means squat anyway. That makes total sense to me now.

Here is an abbreviated sequence, starting after precise focus has been set in Live View:

The one thing I didn't like about it is when your zoomed in while in Liveview even with being as gentle as possible you have to press the two buttons to start the test which makes the focus square dance around a bit . Not cool . They should have figured a way to trigger the process remotely via the ten pin and a menu setting.

Pressing the AF-mode and video-record buttons simultaneously is not what starts the test. It only brings up the dialog box.

I didn't know this either,but you still have to touch the camera to start the test which would still shake the camera little bit, A remote option would've been great.

The test starts after you press OK when the dialog box is displayed.

I've have two more lens to fine-tune I'm going to give your method a try and see how it goes I'm all for saving some time an cutting down on a few steps. Thank you for all your input. Bookmarked.

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- Marianne

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OP Marianne Oelund Veteran Member • Posts: 7,779
Fine tune range - Correction

Marianne Oelund wrote:

Tommi14 wrote:

In the earlier bodies, the range of the AF fine tune is different for the default adjustment and the lens specific adjustment. At least with my D700, setting the default value, for instance, to +10 has a larger effect than setting the lens specific value to +10.

Yes, and this is what I found with all bodies I tested, prior to the D5.

Marianne, what is your feeling, does the range of the auto AF fine tune in D5 correspond to the range of the default adjustment or the lens specific adjustment in the earlier bodies?

My impression is that it is similar to the lens-specific adjustment of earlier bodies, but I need to make a careful check of this as it could well be different. Thanks for asking.

My earlier posts regarding the Default fine tune range for the D5 were incorrect (they were based on a quick test with an f/4 lens, which wasn't a sensitive enough subject).

I've just run some careful tests with an f/1.4, f/2.8 and f/4 lens, and the D5 is similar to older models in this regard:  With f/2.8 or faster lenses, the Default range is about 2.5x as wide as the lens-specific range.  With an f/4 lens, it is around 1.5x.  Presumably with slower lenses, there would be little difference.

Also, comparing the D5 to the D4, there is just a slight difference.  It appears that, if anything, the D5 has a somewhat smaller fine tune range than the D4, perhaps by 10%.  That would make sense, for the D5's finer sensor pitch.

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(unknown member) Contributing Member • Posts: 501
Re: D5 auto AF fine-tune: User notes

Nikon should automate multiple runs and choose the best value. Or run through all values and calculate the optimum, like Reikan Focal does it.

Also the yes/no confirmation should be removed such that you can quickly tune handheld. Consider a wedding photographer who mounts a backup lens and has no tripod available.

Tommi14 New Member • Posts: 6
Re: Fine tune range - Correction

Marianne Oelund wrote:

Marianne Oelund wrote:

Tommi14 wrote:

In the earlier bodies, the range of the AF fine tune is different for the default adjustment and the lens specific adjustment. At least with my D700, setting the default value, for instance, to +10 has a larger effect than setting the lens specific value to +10.

Yes, and this is what I found with all bodies I tested, prior to the D5.

Marianne, what is your feeling, does the range of the auto AF fine tune in D5 correspond to the range of the default adjustment or the lens specific adjustment in the earlier bodies?

My impression is that it is similar to the lens-specific adjustment of earlier bodies, but I need to make a careful check of this as it could well be different. Thanks for asking.

My earlier posts regarding the Default fine tune range for the D5 were incorrect (they were based on a quick test with an f/4 lens, which wasn't a sensitive enough subject).

I've just run some careful tests with an f/1.4, f/2.8 and f/4 lens, and the D5 is similar to older models in this regard: With f/2.8 or faster lenses, the Default range is about 2.5x as wide as the lens-specific range. With an f/4 lens, it is around 1.5x. Presumably with slower lenses, there would be little difference.

Also, comparing the D5 to the D4, there is just a slight difference. It appears that, if anything, the D5 has a somewhat smaller fine tune range than the D4, perhaps by 10%. That would make sense, for the D5's finer sensor pitch.

Thank you so much for the trouble and the information!

Regards,
Tommi

lickity split
lickity split Veteran Member • Posts: 5,431
FoCal link
 lickity split's gear list:lickity split's gear list
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OP Marianne Oelund Veteran Member • Posts: 7,779
Re: FoCal link

lickity split wrote:

Thought you might be interested,

http://www.reikan.co.uk/focalweb/index.php/2016/04/nikon-d500-automatic-af-fine-tune/

Ties up well with my findings.

One detail I noticed is that their result spread is rather high, which from my experience would indicate that their AF target is not optimal. It's fairly easy to get much better consistency than they achieved.

Also, they didn't mention perhaps the most important advantage of the camera's auto fine tune:  You can easily use it in the field, away from a computer.  Having a good AF target in your camera bag would be recommended, though.

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- Marianne

lickity split
lickity split Veteran Member • Posts: 5,431
Re: FoCal link

Marianne Oelund wrote:

lickity split wrote:

Thought you might be interested,

http://www.reikan.co.uk/focalweb/index.php/2016/04/nikon-d500-automatic-af-fine-tune/

Ties up well with my findings.

One detail I noticed is that their result spread is rather high, which from my experience would indicate that their AF target is not optimal. It's fairly easy to get much better consistency than they achieved.

Also, they didn't mention perhaps the most important advantage of the camera's auto fine tune: You can easily use it in the field, away from a computer. Having a good AF target in your camera bag would be recommended, though.

I was kinda of surprised they were not more critical of it considering this is one of Nikon's new features and is ultimately going to be taking some sales away .Its funny how they ended it they basically said it'll get you close but you still need Focal

 lickity split's gear list:lickity split's gear list
Nikon D850 Nikon AF-S Nikkor 24-70mm f/2.8G ED Nikon AF-S Nikkor 300mm f/2.8G ED VR II Nikon AF Micro-Nikkor 200mm f/4D ED-IF Sigma 15mm F2.8 EX DG Diagonal Fisheye +10 more
OP Marianne Oelund Veteran Member • Posts: 7,779
Some AF target evaluations
2

As I mentioned earlier, auto AF fine tune gives the user some insight into the internals of the D5/D500 AF system, specifically, the processing of the AF module signals which produces the focus-error value (which excludes lens-drive characteristics).

Using auto AF fine tune repeatedly produces a set of values, for which the statistical distribution will give a good indication of the consistency of AF for the target in use.  Findings are that various targets definitely do result in different distributions.

For this investigation, I repeated the auto fine-tune procedure 15-20 times for each target, using indirect daylight (window light on a sunny day).  Undesirable targets may produce a range of values where the max-min difference is 15 units or more.  A good target will get that range down to about 6 units, and the very best target I have found has a range of only 3 units.  Here are descriptions for the better targets from my study:

Block Letters

This may be a fairly easy target to find.  It consists of 3 large block letters, black on white, which just fit inside the D5 AF point.  Range 6 units.

Leonard Shepherd's AF Target

This is a small section of the USAF lens resolution test chart.  Leonard gives a recommendation for the printing size, shooting distance and particular area of the chart to use.  Following his guidelines, I examined several adjacent areas, including both white lines on black, black lines on white, and several different sizes of line sets.  Results in all cases showed that about 75% of the values will cluster into a range of about 6 units, which is good, but unfortunately the other 25% of the values tend to be spectacular outliers, very distant from the central cluster of values.  This kind of behavior makes me a little nervous about using this target in earnest.

LensAlign

I have a printed copy of the LensAlign focus target.  Used at about 40x focal length, and aiming at the main central feature, this target gives a reasonably tight distribution ranging across just 6 units.  The distribution of values is fairly even across the range.

Horshack's AF Target

DPReview user Horshack produced an AF target consisting of variable-size crosshatch lines, arranged at random intervals.  I printed this target at size 13x16 cm.  For the first test, I used it at about 12x focal length, which produced good results (range 6 units), but the distribution of the values tended to be end-weighted, i.e., there were not very many results in the center of the range.

Moving back to a distance of 40x focal length, the results improved dramatically.  I was rather amazed to find a distribution range of only 3 units.  I have to give this target my highest recommendation, used at this distance.

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Source credit: Prov 2:6
- Marianne

Leonard Shepherd
Leonard Shepherd Forum Pro • Posts: 17,765
Re: Some AF target evaluations

Marianne Oelund wrote:

Leonard Shepherd's AF Target

This is a small section of the USAF lens resolution test chart. Leonard gives a recommendation for the printing size, shooting distance and particular area of the chart to use. Following his guidelines, I examined several adjacent areas, including both white lines on black, black lines on white, and several different sizes of line sets. Results in all cases showed that about 75% of the values will cluster into a range of about 6 units, which is good, but unfortunately the other 25% of the values tend to be spectacular outliers, very distant from the central cluster of values. This kind of behavior makes me a little nervous about using this target in earnest.

Actually the target I use is not a section of the USAF target, but that is a minor detail.

What would be worth knowing is, have Nikon changed the length of the AF detection lines used in single point AF with the D5/5000? This is easy to check out.

Nikon cautioned about this way back in the era of the F6 when they mentioned the F6 needed larger minimum size targets for AF to work than with the F5 and F100. My photography of flower centres in wild satisfied me Nikon were right and that successful AF on the F100 often required manual focus on the F6.

There were howls of protest from some that AF did not work (as distinct from worked different) when Nikon similarly changed the AF when introducing the D2 series.

Nikon shortened the length of the AF detection lines in the D3s and carried this through to the D7100/7200, D750, D800 and 810. This is the opposite to the way they went with the F6.

I am speculating that the increased number of AF points in the D5/500, including none selectable, enable shorter single detection lines. If this turns out to be right then several AF test targets may need to be used at a lesser focal length magnification factor for best results compared to recent 51 point AF bodies.

The first thing I do when I get a new type of body is to quickly check the length of the single point AF detection lines. If the length is changed a few test shots may be advisable as the new AF system may focus on some things the previous could not, and vice versa.

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Leonard Shepherd
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OP Marianne Oelund Veteran Member • Posts: 7,779
Re: Some AF target evaluations

Leonard Shepherd wrote:

What would be worth knowing is, have Nikon changed the length of the AF detection lines used in single point AF with the D5/5000? This is easy to check out.

I am speculating that the increased number of AF points in the D5/500, including none selectable, enable shorter single detection lines. If this turns out to be right then several AF test targets may need to be used at a lesser focal length magnification factor for best results compared to recent 51 point AF bodies.

It's unavoidable that the detection lines are a little shorter, as the AF point array has no space between points, and the number of points has increased since the D4.

In order to present the D5 AF points with the same detail seen by D4 AF points, the D5 must be moved further away from the target, i.e., at a greater focal length multiplication, not lesser.

The first thing I do when I get a new type of body is to quickly check the length of the single point AF detection lines. If the length is changed a few test shots may be advisable as the new AF system may focus on some things the previous could not, and vice versa.

It is somewhat more complex today.  Often more than one AF point is in use and the camera has sole control over AF points in between the user-selectable points.  Nikon do not describe the detail of the algorithms which determine how the AF points are used, so it is left to the user community to discover them.

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Source credit: Prov 2:6
- Marianne

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