AF accuracy Z lenses vs F lenses on Z9

I am using mostly F-mount lenses, and I notice that with fast lenses, AF can be ever so slightly off.

I was wondering if AF on Z lenses is more accurate - especially with fast lenses.

I understand from experienced colleagues that issues as back/front focus problems are not seen anymore!

Hi Yes, I guess front or back focus is not an issue. I am more thinking of the keeper rate when you shoot at max aperture f1.4 or lower.
It is not close to 100% for me.

I find it lens dependent.
My 58mm f/1.4G behaves far more consistently on a Z-body than F-body so my keeper rate is way up.
For my 105mm f/1.4E, I've not noticed much difference. Never really had an issue on my DSLR and still don't have any issues on my Z6 II.

DSLRs use a mechanism below the mirror for autofocus, so there is always the chance of slight alignment mismatch. That is why you may have to fine-tune F-mount lenses: they are not focusing on the sensor but on a proxy.

Mirrorless cameras have AF sensors included on the image sensor so there is no chance of AF misalignment, so in general it is not necessary to fine-tune any lenses - F-mount or Z-mount.

I find the AF on the Z9 to blow the doors off any of the DSLRs, D5 and D6 not withstanding. When compared to my D850, it is a Night and Day difference. Even the older D810 and D800 were a Night and Day difference compared to the D850.

My question was rather - how many keepers do you get at f1.4 or higher with Z9 - is the hit rate better for Z lenses compared to equivalent F lenses via FTZ adapter both mounted on Z9? I am not asking how it compares with D850.

I understand and agree that mirrorless is better than DSLR for focusing accuracy.

Generally speaking, Yes the keeper rate is very much higher than it was with the D850, about 99.99% better

I think that AF issues with F-mount lenses might be related to the motors used to drive the AF, combined with the electronics driving the motors. I can see circumstances where a motor might slightly overshoot or undershoot when being focused. The stepping motors and electronics in most mirrorless lenses are better matched for the mirrorless AF system; hence they will focus accurately more consistently.

FWIW, I have used various F-mount lenses on Nikon 1 V1 and V2 mirrorless bodies, and have noticed they are usually very accurately focused. But I can also say the same of my D500. Lenses that I needed to do AF fine tuning on my D7000 do not need the same adjustment on my D500. I think that the AF systems in the latest DSLRs have benefited from advances/refinements in DSLR AF technology.

How are you judging "ever so slightly off"?
You seem to have no fast S lenses - and only fast F mount lenses.

Are you expecting to get one third depth of field in front and two thirds behind depth of field - at all focus distances - with apologies if you know this is not true.

Some assume depth of field is always split one third in front and two thirds behind the point of focus.

While this is true when focusing at one third of hyperlocal distance, when we focus closer than one third of HD - more likely wide open with a fast lens - depth of field changes to close to photographically equal (though there is always a mathematical difference) each side of the point of focus as you gradually focus closer.

When focussing at HD (or further away) there is significantly more than two thirds of the available depth of field behind the point of focus.

If you are seeing depth of field closer to equal both sides of the point of focus shooting wide open (or near) with your F mount fast lenses it could be you you are observing the "shape" of depth of field more accurately with mirrorless (down to apertures as small as f5.6) than with DSLR's.

Indeed I lack fast Z mount lenses so I am unable to compare.
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If you are trying to check for focus accuracy, the lens' maximum aperture doesn't matter.

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If you are trying to check for focus accuracy, the lens' maximum aperture doesn't matter.
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If you are trying to determine exactly where the sharpest point is on a subject with depth - especially a ruler at 45 degrees - using the shape of the zone of sharpness either side of the focus point as an aid varies with focal length, focus distance and widest aperture available.

If you are using a fine detail target parallel to the sensor that the AF system can accurately detect then the lens maximum aperture is, as you say, irrelevant.

A measurement on AF fine tune that I did some time ago tells a lot about focus accuracy: There is the systematic error that gets corrected by AF fine tune on some DSLR cameras, and that is mostly not needed on Z cameras (Z7 II and probably other models still have an AF fine tune capability !) . The there is a hysteresis in the focus setting reached, setting depends from which side you start far or close. Finally there are random errors affecting the final focus setting that gets reached. This latter may depend on mechanical friction in the lens and electronic noise in the AF subsystem. My findings are that the Z camera is only very slightly better than my latest DSLR (D850).

let's see if I can successfully upload a graphics image. I cannot see it as I write. It should show focus position at the sensor in micro-meters versus AF tune setting, coming from close (red) or from far (blue). Lens is AF-S 105mm f/1.4 fully open on D850. Green marks best AF tune compromise.

Why do you think so? In the case of mirrorless, there is a contrast detect step after phase detect, I believe that the max aperture does matter.

I didn't quite follow the graph but wanted to understand what you meant above. Are you saying that for a 105mm f1.4 F mount lens, Z cameras are no better than D850 when it comes to focus accuracy?

DSLRs focus wide open. Z cameras don't, unless the taking stop is wide open. That means that Z cameras will do a better job with lenses that have foucs hsift die to spherical aberration.

blog.kasson.com/nikon-z6-7/z7-vs-d850-afs-accuracy-with-nikon-58-1-4/

Why do I think so? Because the point focused on cannot be be unsharp and sharp at the same time.