Z8 Subject Detection Inaccurate in Low (but not that low) light

[j_photo]

It focuses correctly if I manually set the AF point to the eye. If I had to guess I'd say the bug is the PDAF system thinking it's acquired the eye when it hasn't, or the system using the wrong PDAF pixels.

I've been saying off and on for some time that detecting the eye and achieving focus are separate things. The camera is recognizing the eye. But it's not succeeding with focus. It's not unlike when we manual focus: First we must detect the subject then we must adjust focus. It seems the camera's detection abilities exceeds it's focus abilities.

OR that the subject detection system is throwing off the focus system which apparently focuses quite accurately when subject detection is not active. It's the interaction of the two subsystems that seems to be primary here.

Point taken

 

[jimdelves]

Has anyone actually been able to speak to a Nikon representative about this? Presumably they have an official position on optimum settings. Regardless of whether or not the camera can focus in low light, the focus confirmation box should always agree with where the focus actually is. And that, at least, should be a simple FW fix

 

[Dinosaur dave]

It focuses correctly if I manually set the AF point to the eye. If I had to guess I'd say the bug is the PDAF system thinking it's acquired the eye when it hasn't, or the system using the wrong PDAF pixels.

In the video you put on youtube at 70mm it moved the eyebox from right to left eye, and clearly didnt do ANY adjustment to focus, and yet it claimed to have it.

I strongly suspect that the eye detection just does not actually attempt to focus where the box is.

But atleast we can hopefully now put to rest the whole "user error" and "trolls" explanations that are so often given for these things

I would go along with that ..... there's still work to do!

 

[Horshack]

yes but it would tell us something (that I suspect) which is that in lowering light Nikon mirrorless AF relies increasingly on contrast detect which uses defocus ... and my untested conclusion having owned a Z50, Z6ii, and Z8 is that contrast detect checking is triggered excessively by camera movement too small to actually throw focus off enough to warrant the defocus/focus cycle required by the contrast detect "check" ...

Z's only switch to contrast detect as a last resort at the very bottom of their EV range, so it's exceedingly unlikely you'll see it in practice. The videos I posted are in very low light and my Z8 never switched to CDAF.

 

[HyperCypher]

I may be wrong about the transition to contrast detect but I’d still like to see the test done or a test done where the camera is on tripod and the only movement is in the subject. I am wondering if the cameras have accelerometers that initiate AF acquisition … that is what it feels like to me operating the various Nikon mirrorless bodies to me.



I do lots of on tripod work ( real estate ) and just the slightest disturbance of the camera and AF will become active even though distance (phase detect) can hardly have changed at all.

 

[SCoombs]

yes but it would tell us something (that I suspect) which is that in lowering light Nikon mirrorless AF relies increasingly on contrast detect which uses defocus ... and my untested conclusion having owned a Z50, Z6ii, and Z8 is that contrast detect checking is triggered excessively by camera movement too small to actually throw focus off enough to warrant the defocus/focus cycle required by the contrast detect "check" ...

Z's only switch to contrast detect as a last resort at the very bottom of their EV range, so it's exceedingly unlikely you'll see it in practice. The videos I posted are in very low light and my Z8 never switched to CDAF.

How would one tell that it had moved to CDAF? For instance, my understanding is that when using starlight mode this requires that a CDAF confirmation take place on every shot, but I have never noticed any sort of indication of this happening.

 

[Donmonte]

It focuses correctly if I manually set the AF point to the eye. If I had to guess I'd say the bug is the PDAF system thinking it's acquired the eye when it hasn't, or the system using the wrong PDAF pixels.

Yes, that aligns perfectly with my experience with the Z9.

 

[Jimmy G]

Well, I've been following this topic both here and over at FM for some time now and I had been earnestly hoping to see some of the more illustrious Nikon forum, er, "gurus" chime in on this matter and, hopefully, offer their insights and expert troubleshooting skills as to what may or may not be going on here re: the OPs eye-AF experiences.

As someone looking to move from L-mount with a Z8, should I be concerned at this absence of input and feedback? Pricing for this camera has just gotten even more favorable with the new May sale and I'm hoping to make a purchase decision by month's end.

 

[Horshack]

yes but it would tell us something (that I suspect) which is that in lowering light Nikon mirrorless AF relies increasingly on contrast detect which uses defocus ... and my untested conclusion having owned a Z50, Z6ii, and Z8 is that contrast detect checking is triggered excessively by camera movement too small to actually throw focus off enough to warrant the defocus/focus cycle required by the contrast detect "check" ...

Z's only switch to contrast detect as a last resort at the very bottom of their EV range, so it's exceedingly unlikely you'll see it in practice. The videos I posted are in very low light and my Z8 never switched to CDAF.

How would one tell that it had moved to CDAF? For instance, my understanding is that when using starlight mode this requires that a CDAF confirmation take place on every shot, but I have never noticed any sort of indication of this happening.

Set your camera to Pinpoint Area AF Mode and you'll see what CDAF behavior is like - Pinpoint uses CDAF exclusively.

 

[SCoombs]

yes but it would tell us something (that I suspect) which is that in lowering light Nikon mirrorless AF relies increasingly on contrast detect which uses defocus ... and my untested conclusion having owned a Z50, Z6ii, and Z8 is that contrast detect checking is triggered excessively by camera movement too small to actually throw focus off enough to warrant the defocus/focus cycle required by the contrast detect "check" ...

Z's only switch to contrast detect as a last resort at the very bottom of their EV range, so it's exceedingly unlikely you'll see it in practice. The videos I posted are in very low light and my Z8 never switched to CDAF.

How would one tell that it had moved to CDAF? For instance, my understanding is that when using starlight mode this requires that a CDAF confirmation take place on every shot, but I have never noticed any sort of indication of this happening.

Set your camera to Pinpoint Area AF Mode and you'll see what CDAF behavior is like - Pinpoint uses CDAF exclusively.

Yes, I am aware of that but I can't say I've ever noticed a difference in behavior. I will try with greater attention paid.