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

I only had about 20 minutes today to work on this but I received my creepy purchase today and was able to produce the OP's issue, at least believe I have. I'll need to do a more intensive test tomorrow when I have time but here's what I found:
  • Using the same setup but with an EV of 1/160 f/4 ISO 1600/3200, the left eye is consistently OOF
In left eye OOF; could you tell where image was in focus at, or what camera had focused on as shutter was released?

Looking at OP's original images and your test images, you need to add more light to get a closer test. Also sweep hair out of right eye.
 
I only had about 20 minutes today to work on this but I received my creepy purchase today and was able to produce the OP's issue, at least believe I have. I'll need to do a more intensive test tomorrow when I have time but here's what I found:
  • Using the Z8 and the same 24-120 f/4 lens as the OP, the left eye is in focus about 100% in my baseline EV of 1/160 f/4 ISO 400
  • Using the same setup but with an EV of 1/160 f/4 ISO 1600/3200, the left eye is consistently OOF
I'm using AF-C auto-area human face detection with back-button focusing.

On my initial test the problem seems to only occur when the face/eye is at an angle to the camera (and in the low-light EV). It doesn't occur with the face head-on, even in the lower EV case. All of the OPs examples has the baby's face at an angle.

Here are two OOC samples, the first at lower EV and the second at the baseline EV.



What af mode? If it has CSP, this doesn't surprise me as much.
I've seen people use the acronym CSP a lot recently but I must admit to being ignorant of its meaning. What does it mean?
 
I only had about 20 minutes today to work on this but I received my creepy purchase today and was able to produce the OP's issue, at least believe I have. I'll need to do a more intensive test tomorrow when I have time but here's what I found:
  • Using the Z8 and the same 24-120 f/4 lens as the OP, the left eye is in focus about 100% in my baseline EV of 1/160 f/4 ISO 400
  • Using the same setup but with an EV of 1/160 f/4 ISO 1600/3200, the left eye is consistently OOF
I'm using AF-C auto-area human face detection with back-button focusing.

On my initial test the problem seems to only occur when the face/eye is at an angle to the camera (and in the low-light EV). It doesn't occur with the face head-on, even in the lower EV case. All of the OPs examples has the baby's face at an angle.

Here are two OOC samples, the first at lower EV and the second at the baseline EV.
What af mode? If it has CSP, this doesn't surprise me as much.
I've seen people use the acronym CSP a lot recently but I must admit to being ignorant of its meaning. What does it mean?
Closest Subject Priority
 
I only had about 20 minutes today to work on this but I received my creepy purchase today and was able to produce the OP's issue, at least believe I have. I'll need to do a more intensive test tomorrow when I have time but here's what I found:
  • Using the Z8 and the same 24-120 f/4 lens as the OP, the left eye is in focus about 100% in my baseline EV of 1/160 f/4 ISO 400
  • Using the same setup but with an EV of 1/160 f/4 ISO 1600/3200, the left eye is consistently OOF
I'm using AF-C auto-area human face detection with back-button focusing.

On my initial test the problem seems to only occur when the face/eye is at an angle to the camera (and in the low-light EV). It doesn't occur with the face head-on, even in the lower EV case. All of the OPs examples has the baby's face at an angle.

Here are two OOC samples, the first at lower EV and the second at the baseline EV.
What af mode? If it has CSP, this doesn't surprise me as much.
I've seen people use the acronym CSP a lot recently but I must admit to being ignorant of its meaning. What does it mean?
Closest Subject Priority
Ahh, this makes sense.

I don't know about Horshack's examples, but in the vast majority of my cases there is no closest object that could be distracting the AF.
 
As a fellow dance photographer, thank you for your comment.

I started back with an FM2 and an F3, back in the days of tracking a dancer in live performance on a stage with manual focus and film, hoping Ektapress 1600 done by a competent lab might net you something useful LOL. Fun times! Back then, we used to practice follow focus (manual) on cars over an overpass. Probably couldn't do that today with all the nut jobs, but it helped hone the muscle memory.

I'm not the only studio shooter having issues. In fact, most folks I know locally who shoot Nikon in the studio gave up on the Z bodies for such and went back to the D850 or D810/D800 series. A few moved on to Canon or Sony. There was a guy in the forums who I believe has discontinued his account - Ray "BurnImage", who have to move to Sony from Nikon because of this problem and I think part of the reason he left was getting tired of pointing out a real problem experienced by many but so many saying none of us knew what we were doing. Point being, I'm far from the only one having the issue.

What I think helps is obviously increasing the ambient light so the EVF/Focus stream on the Z8 gets better data to work with, and I'm guessing (but have not tested) going with a focus assist LED that is daylight balanced might help. Sadly I can't "upgrade"/"Switch" out my Elinchrom modelling lamps to an LED replacement, at least I haven't found out a compatible sub-out and I spent some time looking.

For point of reference, most all my studio is shot at F/9 with an ambient EV of about 6 to about 7. I really don't want to resort to blinding a model with crazy bright focus assist, but I will try one next time around.

I'm not going to change how I use AF from AF-S to AF-C because it makes zero sense for a static model - and the Z cameras, they're not seeing motion, only portrait or fashion. The other thing is pretty simple and pragmatic: I'm older now, and after starting shooting dance in 1985, I've done what I've done and the studio work is way down to the point where I'm strictly doing personal work these days. I don't shoot live performance any longer, and occasionally shoot some outdoor personal work with dancers.

I'm probably more interested in doing some video work with them in the future. So that means I don't "need" the Z8 or Z bodies to be as good as the D850, because I already have the D850 and kept a few core lenses around, and it's essentially perfect in the studio - achieving 99%+ hit rates on anything I throw at them. But I do love the Z lenses - particularly the mid tele's (85/1.2S, 105/2.8MC, 135 Plena) as those are some of the very best glass I've used in 40+ years from any manufacturer (and I've shot about everything), so I welcome improvement in studio AF.

I think things will improve. Over time, I'll do more testing. The 2.00 firmware on the Z8 seemed to improve things a little bit. Who knows what Nikon is doing behind the scenes. I am perplexed as much as anyone; I mean, even after objective tripod based test chart focus series and seeing the variance even in AF-S with focus priority and all the right settings be much higher than the D850, something is going on. Just a matter of finding out what and how to best work around it.

Take care and good luck shooting.
 
Hi, a lot of what is being discussed here resonates with me and i have generally blamed myself for it. I often try to work out where i might have gone wrong and i usually can see if it was my mistake, but there are occasions where i just don't know what is the cause of a missed focus where i thought i had conditions in my favour. I have Z8 and an 800mm Z PF and have my shutter button half press set for Auto Area AF, which i find acquires initial focus quicker than anything i have tried so far and seems to lock focus as well as 3D afc with the situations i use it with. I have BBAF set to 3D afc and one of the front Fn buttons to single point afc and all of these modes with subject detection on. I photograph Birds predominately. There have been some interesting suggestions here that i need to try and implement and thank those who have contributed. I remember a long time ago when i had an Olympus EM1 which also had a hydrid af system and i got frustrated with it at times and wondered if the cause or part of the cause was that there were no cross-point focus points to help things, same as my Z8. I didn't seem to have these issues with my previous Nikon cameras; D750,D500,D850 and also with these i really liked the group area focus mode that i felt worked better than the dynamic area modes. I know i have more to learn even after thousands of photos and owning this setup for six months. I have taken some great photos with my current gear but i'm just after a little bit more reliability with focus. This just an opinion but feel free to correct me in any way. Again thanks to the OP for bringing this up and taking the time to help others.

Cheers Shane
 
I did take a lot indoor photos for my little daughter, 50mm f/1.8, AF-C, people detection, BBF, SS 1/250 or even faster, auto ISO (2000-12,800). I think the overall lighting condition is worse than your example, the hit rate is 70% and higher, maybe ~80%.

I also used 24-120 but the ISO seems too high so 50 1.8 is my main indoor lens, but I dont remember seeing a horrible hit rate with 24-120.

Did you try a faster SS to see if it helps or not? I remember the MF ring on lens was too sensitive so I had to disable it.
 
For point of reference, most all my studio is shot at F/9 with an ambient EV of about 6 to about 7
I'm not very active on the forum, just lurking, but I'll chime in here.

Thanks to SCoombs for an interesting post. I've been a photographer since the early '90s, event and studio photography with Elinchrome flashes. I went digital in 2000. However, when using the Z series cameras in the studio, I encountered focusing issues. The Z6 and Z7 wouldn't focus with face detection at settings I usually used with the D810 and f/5.6 aperture. After some frustration, I found out, not without some struggles, that I needed about EV 7 in the ambient light for satisfactory focus. At EV 7, I could get 5 out of 5 shots in focus. EV 6 resulted in approximately 3 out of 5 in focus, EV 5 only 1 out of 5, and EV 4 none in focus. EV 7 provides a lot of light at f/5.6, almost blinding the model, so dropping down to f/4.0 helps. However, this requires using the Elinchrome at its lowest power setting (but then other problems arise, like slow flash duration). Now, I've had the Z8 for over half a year, and I haven't found much improvement compared to the Z6 and Z7 in this regard. The Z8 also needs EV 7 for proper focus. I want to emphasize that my tests are informal, based on how I set up the equipment.

I believe that to have a reasonable discussion about autofocus errors with flash and subject detect , it might be helpful if people mention the EV value when complaining about misfocus. For example, we don't know the EV value that the thread starter SCoombs had; "Low (but not that low) light."

Lastly, I must mention that English is not my native language, so I had to use ChatGPT to make it all understandable :-)
 
For point of reference, most all my studio is shot at F/9 with an ambient EV of about 6 to about 7. I really don't want to resort to blinding a model with crazy bright focus assist, but I will try one next time around.
You don’t have to. I’m using a 300w LED at 10-20% power, about 15ft away and it absolutely helps for the Z6. About 90% of my work is 5.6-8 on the 24-120 f/4. I miss focus maybe 1 out of 50 shots.
 
I only had about 20 minutes today to work on this but I received my creepy purchase today and was able to produce the OP's issue, at least believe I have. I'll need to do a more intensive test tomorrow when I have time but here's what I found:
  • Using the Z8 and the same 24-120 f/4 lens as the OP, the left eye is in focus about 100% in my baseline EV of 1/160 f/4 ISO 400
  • Using the same setup but with an EV of 1/160 f/4 ISO 1600/3200, the left eye is consistently OOF
I'm using AF-C auto-area human face detection with back-button focusing.

On my initial test the problem seems to only occur when the face/eye is at an angle to the camera (and in the low-light EV). It doesn't occur with the face head-on, even in the lower EV case. All of the OPs examples has the baby's face at an angle.

Here are two OOC samples, the first at lower EV and the second at the baseline EV.
What af mode? If it has CSP, this doesn't surprise me as much.
I've seen people use the acronym CSP a lot recently but I must admit to being ignorant of its meaning. What does it mean?
Closest Subject Priority
None of the focus modes have closest subject priority when subject recognition is active. The wide area modes do have closest subject priority when subject recognition is not active, or if it has not found a subject (box hasn't stepped down).

Similarly, 3D does not track the color/contrast under the focus point when subject recognition is active.

The AF functions EITHER as described in the focus mode chart, OR it functions as subject recognition/tracking... it can't do both.


When subject recognition is active it picks what it believes is the best subject; sometimes it gives you a choice between multiple subjects.

--
https://www.flickr.com/skersting
 
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For point of reference, most all my studio is shot at F/9 with an ambient EV of about 6 to about 7
I'm not very active on the forum, just lurking, but I'll chime in here.

Thanks to SCoombs for an interesting post. I've been a photographer since the early '90s, event and studio photography with Elinchrome flashes. I went digital in 2000. However, when using the Z series cameras in the studio, I encountered focusing issues. The Z6 and Z7 wouldn't focus with face detection at settings I usually used with the D810 and f/5.6 aperture. After some frustration, I found out, not without some struggles, that I needed about EV 7 in the ambient light for satisfactory focus. At EV 7, I could get 5 out of 5 shots in focus. EV 6 resulted in approximately 3 out of 5 in focus, EV 5 only 1 out of 5, and EV 4 none in focus. EV 7 provides a lot of light at f/5.6, almost blinding the model, so dropping down to f/4.0 helps. However, this requires using the Elinchrome at its lowest power setting (but then other problems arise, like slow flash duration). Now, I've had the Z8 for over half a year, and I haven't found much improvement compared to the Z6 and Z7 in this regard. The Z8 also needs EV 7 for proper focus. I want to emphasize that my tests are informal, based on how I set up the equipment.

I believe that to have a reasonable discussion about autofocus errors with flash and subject detect , it might be helpful if people mention the EV value when complaining about misfocus. For example, we don't know the EV value that the thread starter SCoombs had; "Low (but not that low) light."

Lastly, I must mention that English is not my native language, so I had to use ChatGPT to make it all understandable :-)
It is relevant to note that the Z camera's low light AF rating is based on using a very fast lens set to the maximum aperture (f/1.2 for Z9). If you are starting at EV7 and stopping down to f/9 the camera is seeing less than EV2; which is quite dark. EV2 is well within the camera's low light capability, but it becomes MUCH more dependent on the quality of the focus area in terms of contrast (which includes size to some degree).

I.e. if you give the focus point a high contrast target of larger vertical black and white lines it will be more accurate in lower light conditions.
 
For point of reference, most all my studio is shot at F/9 with an ambient EV of about 6 to about 7
I'm not very active on the forum, just lurking, but I'll chime in here.

Thanks to SCoombs for an interesting post. I've been a photographer since the early '90s, event and studio photography with Elinchrome flashes. I went digital in 2000. However, when using the Z series cameras in the studio, I encountered focusing issues. The Z6 and Z7 wouldn't focus with face detection at settings I usually used with the D810 and f/5.6 aperture. After some frustration, I found out, not without some struggles, that I needed about EV 7 in the ambient light for satisfactory focus. At EV 7, I could get 5 out of 5 shots in focus. EV 6 resulted in approximately 3 out of 5 in focus, EV 5 only 1 out of 5, and EV 4 none in focus. EV 7 provides a lot of light at f/5.6, almost blinding the model, so dropping down to f/4.0 helps. However, this requires using the Elinchrome at its lowest power setting (but then other problems arise, like slow flash duration). Now, I've had the Z8 for over half a year, and I haven't found much improvement compared to the Z6 and Z7 in this regard. The Z8 also needs EV 7 for proper focus. I want to emphasize that my tests are informal, based on how I set up the equipment.

I believe that to have a reasonable discussion about autofocus errors with flash and subject detect , it might be helpful if people mention the EV value when complaining about misfocus. For example, we don't know the EV value that the thread starter SCoombs had; "Low (but not that low) light."

Lastly, I must mention that English is not my native language, so I had to use ChatGPT to make it all understandable :-)
It is relevant to note that the Z camera's low light rating is based on using a very fast lens at it's maximum aperture (f/1.2 for Z 8/9). If you are starting at EV7 and stopped down to f/9 the camera is getting less than EV2... that is quite dark.

Yes, EV2 is well within the camera's AF capability specification, but it will be much more dependent on the quality (size/contrast) of the focus area provided. I.e. if you give it a high contrast target of larger vertical black and white lines to focus on it will be more accurate in lower light conditions.

--
https://www.flickr.com/skersting
 
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It seems extraordinary that a company with resources such as Nikon cannot reverse engineer an A9ii or A1 and use that AF. I’m not a professional, but if I was I doubt I’d bother waiting for them to catch up
 
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For point of reference, most all my studio is shot at F/9 with an ambient EV of about 6 to about 7. I really don't want to resort to blinding a model with crazy bright focus assist, but I will try one next time around.
You don’t have to. I’m using a 300w LED at 10-20% power, about 15ft away and it absolutely helps for the Z6. About 90% of my work is 5.6-8 on the 24-120 f/4. I miss focus maybe 1 out of 50 shots.
From looking at your website, you're using A LOT more natural light than most studio work or other photographers do. Having used the Z8 and ZF, there is NO comparison to Sony's eye detection or subject tracking. Even their 2019 AF-C is as good as Nikon flagships.
 
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I must admit that I do not know how to calculate an objective EV value. I can offer a few things. First, a handful of examples from my most recent test can be found here, including some taken with the camera calculating the exposure with no flash and which can be used to determine the objective lighting conditions from THIS test: https://drive.google.com/drive/folders/1CPVtXNAfrPp8FI3ovWep5pR09o2l4OSG?usp=drive_link

However this test was a bit better than before. Details on that below.

Second, based on one photo I have from the prior tests with no flash, I think the correct exposure for that situation would have been in the area of 1/160 f4 ISO 3200 +2EV.

The original photos that I started the thread with were taken in an EV equating to 1/160, f2.8, ISO 400, flash at 1/4 -.33 at 200mm, focus distance recorded as 2.02 m.

Now, as to the update on the latest tests ((the ones that I posted files from above):

Today I installed the 2.01 firmware and when I sat down to get a few samples of this problem I noticed that the focus was behaving more consistently. I took around 100 shots, about 80% with flash, mixing subject detect and single point. My initial impression reviewing on camera was that it was behaving much better than it had been. It looked like almost everything was a focus hit.

When I put them into NX Studio for review I found the truth is a bit more mixed than that. On the one hand, I would say that it did behave better. On the other hand, it was still off about half the time or more.

The big difference, and the reason I thought when reviewing on camera that it was much better, is that a much smaller number of the shots are such significant misses that it winds up with the entire person out of focus. Most are misses where careful examination will reveal that the wrong eye is in focus but there's really just a slight difference between the two eyes so that when viewed at a more normal size it might be missed. Some are misses when the wrong eye is in tack sharp focus, and in these cases the other eye is totally out of focus. A handful missed badly so that the ear is in focus or something else altogether in front of or behind the person.

Of course, this probably means that critical focus is still being missed. This is because when the focus is where it should be, the depth of field is such that the in focus eye is sharp while the other eye is totally out of focus. When the focus misses more significantly, the wrong eye is in sharp focus and the eye that had the AF point on it is totally out of focus. Therefore, when both eyes look okay with one slightly better, it probably means that the focus has actually missed somewhere in the middle.

This also agrees with some of Horshack's findings. One, it wasn't really missing (at least not tonight; it did before) when the person was square to the camera. Two, when it did miss it most of the time missed by focusing on the wrong eye.

Now this was just one quick test and I may try it again and find it working again like it did before. However, if the results of this test are accurate - and they do agree with Horshack's results so far - then it would seem to indicate that what is causing the out of focus effect may be that the system is somehow "behind scenes" just plain focusing on the other eye. This would also perhaps explain why the system seems to perform better with single point (though I didn't get much success with that at my event last night): because the actual focusing is working correctly, but the subject detection is for some reason sometimes telling the system to focus on a different eye from the one it reports.
 
For point of reference, most all my studio is shot at F/9 with an ambient EV of about 6 to about 7
I'm not very active on the forum, just lurking, but I'll chime in here.

Thanks to SCoombs for an interesting post. I've been a photographer since the early '90s, event and studio photography with Elinchrome flashes. I went digital in 2000. However, when using the Z series cameras in the studio, I encountered focusing issues. The Z6 and Z7 wouldn't focus with face detection at settings I usually used with the D810 and f/5.6 aperture. After some frustration, I found out, not without some struggles, that I needed about EV 7 in the ambient light for satisfactory focus. At EV 7, I could get 5 out of 5 shots in focus. EV 6 resulted in approximately 3 out of 5 in focus, EV 5 only 1 out of 5, and EV 4 none in focus. EV 7 provides a lot of light at f/5.6, almost blinding the model, so dropping down to f/4.0 helps. However, this requires using the Elinchrome at its lowest power setting (but then other problems arise, like slow flash duration). Now, I've had the Z8 for over half a year, and I haven't found much improvement compared to the Z6 and Z7 in this regard. The Z8 also needs EV 7 for proper focus. I want to emphasize that my tests are informal, based on how I set up the equipment.

I believe that to have a reasonable discussion about autofocus errors with flash and subject detect , it might be helpful if people mention the EV value when complaining about misfocus. For example, we don't know the EV value that the thread starter SCoombs had; "Low (but not that low) light."

Lastly, I must mention that English is not my native language, so I had to use ChatGPT to make it all understandable :-)
It is relevant to note that the Z camera's low light AF rating is based on using a very fast lens set to the maximum aperture (f/1.2 for Z9). If you are starting at EV7 and stopping down to f/9 the camera is seeing less than EV2; which is quite dark. EV2 is well within the camera's low light capability, but it becomes MUCH more dependent on the quality of the focus area in terms of contrast (which includes size to some degree).
I.e. if you give the focus point a high contrast target of larger vertical black and white lines it will be more accurate in lower light conditions.
Backing up a bit further, several commenters have reverted to their D850s or other f-mount body and lens. If I'm not mistaken the Z cameras focus at set aperture until it reduces beyond f/5.6, at which point they focus at f/5.6. This is essentially the same as what happens with an f-mount camera for most focus points in the frame. So I'd say that the Z-body is seeing not EV2 but EV3.3. We have to be careful comparing f-mount to Z because the f-mount body's effective AF aperture is far smaller than the main lens.
 
For point of reference, most all my studio is shot at F/9 with an ambient EV of about 6 to about 7
I'm not very active on the forum, just lurking, but I'll chime in here.

Thanks to SCoombs for an interesting post. I've been a photographer since the early '90s, event and studio photography with Elinchrome flashes. I went digital in 2000. However, when using the Z series cameras in the studio, I encountered focusing issues. The Z6 and Z7 wouldn't focus with face detection at settings I usually used with the D810 and f/5.6 aperture. After some frustration, I found out, not without some struggles, that I needed about EV 7 in the ambient light for satisfactory focus. At EV 7, I could get 5 out of 5 shots in focus. EV 6 resulted in approximately 3 out of 5 in focus, EV 5 only 1 out of 5, and EV 4 none in focus. EV 7 provides a lot of light at f/5.6, almost blinding the model, so dropping down to f/4.0 helps. However, this requires using the Elinchrome at its lowest power setting (but then other problems arise, like slow flash duration). Now, I've had the Z8 for over half a year, and I haven't found much improvement compared to the Z6 and Z7 in this regard. The Z8 also needs EV 7 for proper focus. I want to emphasize that my tests are informal, based on how I set up the equipment.

I believe that to have a reasonable discussion about autofocus errors with flash and subject detect , it might be helpful if people mention the EV value when complaining about misfocus. For example, we don't know the EV value that the thread starter SCoombs had; "Low (but not that low) light."

Lastly, I must mention that English is not my native language, so I had to use ChatGPT to make it all understandable :-)
It is relevant to note that the Z camera's low light AF rating is based on using a very fast lens set to the maximum aperture (f/1.2 for Z9). If you are starting at EV7 and stopping down to f/9 the camera is seeing less than EV2; which is quite dark. EV2 is well within the camera's low light capability, but it becomes MUCH more dependent on the quality of the focus area in terms of contrast (which includes size to some degree).
I.e. if you give the focus point a high contrast target of larger vertical black and white lines it will be more accurate in lower light conditions.
Backing up a bit further, several commenters have reverted to their D850s or other f-mount body and lens. If I'm not mistaken the Z cameras focus at set aperture until it reduces beyond f/5.6, at which point they focus at f/5.6. This is essentially the same as what happens with an f-mount camera for most focus points in the frame. So I'd say that the Z-body is seeing not EV2 but EV3.3. We have to be careful comparing f-mount to Z because the f-mount body's effective AF aperture is far smaller than the main lens.
I thought F-mount cameras always focused wide open. I know I personally tested this on my f1.8 35mm and my D500, with the camera focusing at f1.8 no matter what aperture I had set.
 
DSLR cameras focus with the lens technically wide open, but the AF system see's the cone of light as if the lens was stopped down to F/5.6 or so. There's some technical explanations of this from Marianne Oelund on this site somewhere - don't have the link handy.
 
DSLR cameras focus with the lens technically wide open, but the AF system see's the cone of light as if the lens was stopped down to F/5.6 or so. There's some technical explanations of this from Marianne Oelund on this site somewhere - don't have the link handy.
Correct.

Marianne's opus is now on Photonstophotos.net.
 
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DSLR cameras focus with the lens technically wide open, but the AF system see's the cone of light as if the lens was stopped down to F/5.6 or so. There's some technical explanations of this from Marianne Oelund on this site somewhere - don't have the link handy.
As far as I know the Sonys focus wide open. So that might be a reason for the bad performance of the Nikon Zs. I am also having troubles in the studio with the Z6, shooting at f8. Outside in good light performance is excellent.
 

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