D850 AF Fine Tune error

[Malcolm Payne]

Sorry, another D850 question:

I have a Micro-Nikkor 105G lens that appears as if the focus may be slightly 'off' in normal phase-detect AF mode. I've repeatedly attempted the AFFT tuning procedure but every time I get an error message, 'Autofocus Fine Tune cannot be used with the current focus settings', or similar. I'm using a good AF target with plenty of light and have double checked that all the settings are correct and followed the instructions precisely but still get the same error every time.

A Google search turns up plenty of reports from others with the same issue but no-one seems to have a solution that actually works, at least for me. I've even tried a full factory reset on the basis of one suggestion, but no joy.

Has anyone here found the same problem and hopefully also a solution?

Many thanks.

[E.J. Peiker]

You get that if you aren't in AF-S, single point mode (without any expansion so no d25, d72, etc), and you must be on the center AF point.  If you move even one point off of the center you will get that error.

[Malcolm Payne]

If you move even one point off of the center you will get that error.

Thank you, that was the clue I needed. Light bulb moment: I had been focussing in Live View using the touch screen to disturb the camera as little as possible, but the tiny shift in the focus point that inevitably caused was obviously sufficient to disrupt the whole process.

The AFTT process, and particularly its extreme sensitivity to procedural minutiae, is not well documented; that should be a prominently highlighted caveat.

Thanks again - I greatly appreciate your help.

[Jim Kasson]

The AFTT process, and particularly its extreme sensitivity to procedural minutiae, is not well documented; that should be a prominently highlighted caveat.

FSS has a few gotchas, too.

https://blog.kasson.com/d850/nikon-d850-focus-shift-with-1051-4/

Jim

[E.J. Peiker]

Thank you, that was the clue I needed. Light bulb moment: I had been focussing in Live View using the touch screen to disturb the camera as little as possible, but the tiny shift in the focus point that inevitably caused was obviously sufficient to disrupt the whole process.

The AFTT process, and particularly its extreme sensitivity to procedural minutiae, is not well documented; that should be a prominently highlighted caveat.

Thanks again - I greatly appreciate your help.

Glad it helped.  I ran into the same problem initially on the D500.  In the end though, I was disappointed by the consistency of the automatic AFFT function and went back to a manual process using a tethered tablet and shooting a Lens Align II target with long ruler.

[Malcolm Payne]

I used the recommended method of taking a dozen readings, discarding the top and bottom values and averaging the remainder. For what it's worth, when I finally got it working, the consistency of adjustment in the 105 Micro was extremely stable, varying by only 1 point over the sequence and with an average value of -12. Though I don't know how well that consistency correlates to accuracy of adjustment in practice.

The 60mm Micro that I tried subsequently was initially far less consistent, bouncing all over the place from +3 to +20. I refocused that one and tried again with better results, the bulk of the run being stable around +12 but with several outliers at +19.

For my art repro work where focus is absolutely critical I use Live View anyway, so any slight inaccuracy in the PD autofocus system isn't an issue; unfortunately the sculpture photography project for which the D850 was purchased won't permit that luxury, so accurate push-button focus is a necessity.

On the back of your comment I'm minded also to try the manual method later when I have more time, if only for confirmation, but hopefully the auto adjustment will be 'close enough' for the purpose.

[E.J. Peiker]

My work was all with super telephoto lenses in the 400 to 800mm range - opposite end of the spectrum from you

[Jim Kasson]

For my art repro work where focus is absolutely critical I use Live View anyway, so any slight inaccuracy in the PD autofocus system isn't an issue; unfortunately the sculpture photography project for which the D850 was purchased won't permit that luxury, so accurate push-button focus is a necessity.

Then you may wish to consider another camera system for that project.

[Malcolm Payne]

Thanks for the further information, Jim. That's pretty damning. Lens or body issue? Single sample?

Too late now anyway. The spec was for 30MP minimum and it had to be a Nikon body, if only to work with existing lenses; there isn't the budget to replace those.

'Accurate' is a relative term in this instance: hopefully the depth of field necessary for 3D sculptures will be sufficient to mask any variation or minor discrepancies in the fine tuning, though it will still be a pain if it misses the focus point.

I shall do some further testing over the weekend with your results in mind.

[Jim Kasson]

Thanks for the further information, Jim. That's pretty damning. Lens or body issue? Single sample?

I've tested many lenses and several bodies. In my experience, the D850 is no better and no worse in this regard than the D5. It's an inherent problem with PDAF in DSLR's, which can't correct for focus shift even if they are perfectly AF-tuned, and can't focus as consistently accurately as on-sensor CDAF trimming.

Jim